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Since upgrading to Sierra (but could be other cause), my mouse slows down in certain points (as if something is intercepting the mouse move event and swallowing it). Sometimes this is accompanied by mouse cursor blinking between rapidly between different cursor shape, in a certain point which allows drag&drop (only/especially when drag is started); then the mouse pointer becomes "stuck" as if moving in dense syrup, for a few seconds/pixels. But this happens as well when not drag&dropping as well. Though, the effect is weaker (though still negatively affects productivity).

An extreme case is when doing native HTML5 drag in Chrome...

Please note: this is not about scrolling (unlike some questions which seem similar).

MacBook Pro Retina 13", late 2013. Two external DisplayPort monitors.

If this could be blamed on an app (as opposed to macOS sierra itself), then which kinds of apps would have such power to intercept and affect mouse-move events? Personally in my multiple decades of computing, I've never seen mouse-move being affected in such a way. Usually the mouse was moving the way it should...

Tried Safe Mode (holding shift while booting), but it completely fails to load (progress bar stuck at 100%)...

Time for a new macbook? Or time to go to Windows? :)

This is ruining my productivity (mouse moving at random speeds, sometimes 2-10 times slower).

Thanks for any hints! Does affect magic mouse 2 and logitech usb-cable mouse.

Problem does not seem to happen on MacBook's touchpad.

  • Right now what happened is that logitech usb-cable mouse is not affected at all, while magic mouse 2 is heavily affected. This happened after terminating karabiner grabber process. Not sure if related or just coincidence. The problem is quite random, thus perhaps Karabiner had nothing to do with it... – KarolDepka Apr 30 '17 at 0:02
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    I've just posted an answer. However, as an aside, since you've stated both here and in your other question that you can't boot into Safe Mode, I really think you should search for answers to that, and if you can't find one, ask another question relating to it. Being able to boot into Safe Mode is a key troubleshooting step, and it would be handy for both your questions. – Monomeeth Apr 30 '17 at 0:51
  • Good point. Upvoted. I just fear another rabbit hole. I recently had waaay too many rabit hole/ troubleshootings. Fearing that getting safe mode to work could turn into another "research project" of its own. Especially that I had problems with filesystem corruption which was somehow related to FileFault, requiring de-encrypting (no one found the real root cause, including apple-authorized tech support; just workaround; decrypting and re encrypting which then makes the problem reappear anyway). And the rabbit hole goes on and on. I hope you understand, I'm a bit tired of rabbit holes :). – KarolDepka Apr 30 '17 at 2:34
  • I'm also thinking of getting a new macbook pro retina. Which would give me fresh install, fresh FS, etc. But then who knows what problems will appear there. Optimism bias could mean tens of hours spent instead of saved :D. – KarolDepka Apr 30 '17 at 2:35
  • Asked about the safe mode problem: apple.stackexchange.com/questions/282315/… – KarolDepka Apr 30 '17 at 2:40
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I just found this because I had the same problem. I noticed that the cursor would come to a crawl whenever I hovered across a list of links on a website. The culprit: I had my mouse cursor set to a larger size. Solution: Go to System Preferences › Accessibility › Display, and set the cursor size to Normal (all the way to the left). After restarting Safari, the problem was gone. I can move across a list of links, the cursor switches between arrow and hand, without lag.

  • I joined the site just to upvote this. I think it would be instructive to know how you found this out. – Roy Falk Feb 13 '18 at 11:10
  • @RoyFalk I have a friend with the exact same MacBook Pro as me. He considered buying the same external display that I have, so he came over to try it out. He used his MacBook Pro with my Display, and we were surprised to find that the problem didn't occur. I then checked which settings were different on his one, and after a lot of searching I found that it was the cursor size. Fun sidenote: If menus fade out in a jerking way on your external display, that's because you have "Reduced Transparency" or "Increase Contrast" set to On in your System Preferences ;-) Oh Apple. – basteln Feb 15 '18 at 14:28
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    Since I've increased the cursor size I've noticed the exact same issue e.g. using iTunes search field. It's a Sierra bug. It's not related to your mouse or external monitor. Pram, smc or booting in safe mode doesn't work. Simply change the cursor size back to normal. I am going to open a Apple bug report. – howdytom Mar 3 '18 at 22:37
  • Crazy that this would cause such a weird issue. Is it because the pointer changes size? I also had this problem, but thought it was some kind of feature at first -- to assist with honing in on links. – lericson Nov 5 '18 at 12:29
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Since you can't seem to boot into Safe Mode, I would try either (or both) resetting the NVRAM and trashing the Magic Mouse .plist files.

Resetting the NVRAM

Your Mac uses Non-Volatile Random-Access Memory (NVRAM).

Here’s how to rest it on your model MBP:

  1. Shut down your machine. Yes, a full shut down, not just logging out.
  2. Press the power button and then press the commandoptionpr keys. You have to make sure you press these keys before the gray screen appears or it won’t work.
  3. Hold those keys down until your Mac reboots again and you here the startup chime.
  4. Let go of the keys and let your Mac reboot normally.

Note: When you log back in you may need to readjust some of your system preferences (e.g. speaker volume, screen resolution, startup disk selection, time zone information, etc).

Trash Magic Mouse .plist files

Since your issue persists both in and out of Safe Mode, I would trash the relevant Magic Mouse preference files.

As you don't specify what version of macOS you're using, I'll assume you're running a version from Mountain Lion and above. Follow these steps:

  1. Go to Finder
  2. Press and hold the option key
  3. While keeping the option key down, click on the Go menu and select Library from the list
  4. This should open up your user's Library folder in a new Finder window
  5. Locate and open the Preferences folder (it's within the Library folder)
  6. Within this folder find the following two .plist files:
    • com.apple.AppleMultitouchMouse.plist
    • com.apple.driver.AppleBluetoothMultitouch.mouse.plist
  7. Now Trash these files
  8. Restart your Mac

Your Mac will now create a new set of default preference files for your Magic Mouse.

Note: You will need to go back to System Preferences and reconfigure your Magic Mouse settings. However, before doing that I would test the Magic Mouse first to see if the problem behaviour still persists.

[EDIT - following successful Safe Mode boot]

Since you've now been able to boot into Safe Mode and the problem wasn't present, the first thing to do is to startup normally and see if the problem is still there. Sometimes just the act of booting into Safe Mode will resolve the issue.

If the problem is still there, the first thing I'd check is your login items. Login items can be incompatible sometimes with other software/hardware.

To do this:

  1. Go to Apple > System Preferences
  2. Click on Users & Groups
  3. In the lefthand pane, select your user name
  4. Now select the Login Items tab (near top right)
  5. Take a screenshot of the list that appears (ShiftCommand4 and select the list with your mouse cursor) or just write down the list
  6. Now click on the first item in the list so it's highlighted (i.e. click on the name, not the checkbox)
  7. Press and hold the Shift key while you click on the last item in the list
  8. All items should be selected now.
  9. Let go of the Shift key
  10. Click on the minus - button (at the bottom) to remove all items
  11. Exit System Preferences
  12. Restart your Mac

Once your Mac has booted up, test to see if your mouse is now working properly:

  • If your mouse works fine, then start to add the items back one by one (using your list or screenshot). However, only add one item at a time and restart your Mac after each one. This process will help you identify which item was causing your mouse problems. Once you know which item it is, then remove that again from your Login Items.
  • If your mouse doesn't work fine, let us know.
  • Thanks. I will try that soon. Regarding safe mode, I did not manage to enter it (hangs before logging in)! In general: do you have an idea what the real root cause could be? – KarolDepka Apr 30 '17 at 1:31
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    Since I'm quite caucious about doing stuff like resetting nvram or deleting plist file: I would like to ask you: what leads you to believe that the mouse slowing down has something to do with nvram or plist files? Instead of e.g. some faulty app or driver messing up input events? Meaning I gotta be sure that it's worth the hassle and the risk, so as not to mess it up even worse :D! Thanks! – KarolDepka Apr 30 '17 at 1:44
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    You don't need to do both - do one and if that doesn't resolve your issue, then try the other. Resetting the NVRAM is no big deal - it's a troubleshooting step that's been used on Macs for decades. In terms of trashing the .plist files, you can make a copy of them first and replace them again later if you're concerned. As for why I'm suggesting these courses of action, well, troubleshooting is a process of elimination, so we need to start somewhere. Since you can't boot into Safe Mode, this is just where I'm suggesting you start. Otherwise my first step would be Safe Mode. – Monomeeth Apr 30 '17 at 1:57
  • Thanks. Great explanation! Upvoted. Given the elimination approach, I sense that we don't [yet] have any hints regarding the possible real root cause(s), right? Will try your approaches soon. – KarolDepka Apr 30 '17 at 2:30
  • By the way, if you do reset the NVRAM this may also help with your other question (re: LG monitor issue). – Monomeeth Apr 30 '17 at 5:29

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