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I have two identical Lenovo P24h-10 monitors plugged into my Macbook. Each one has it's own USB-C cord. I thought about using a single Display Port cord and then daisy-chaining them together, but each monitor has USB outlets that I'm using to connect my peripherals so I don't need a separate hub. I've noticed there is a 50% chance that the display arrangement will be flipped every time my computer wakes from sleep. I think this is because there is no way for my computer to differentiate between the two. Is there a way to set a name on my monitors?

In the Display Preferences, each monitor is listed as P24h-10 (1) and P24h-10 (2), and they can change.

This seems like a really silly problem to have. I'm hoping there is an easy fix, but I've been scouring the internet for weeks now looking for some help. Any thoughts?

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    If no one else offers suggestions, have you tried an HDMI cable? This monitor offers one and with a USB > HDMI adapter that might solve the problem. Just guessing here, so if you buy an adapter make sure you can return it... Jul 20 '20 at 17:21
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    I've thought about doing that, but then I would lose the ability to plug in my peripherals into that monitor.
    – bheussler
    Jul 20 '20 at 18:00
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I've experienced this as well, and there are a few fixes that I've found.

Solution One This fix involves involve running macros on startup. Here's a link to the "Keyboard Maestro" method which includes using a utility called displayplacer on github.

Solution Two It's possible this is related to spaces/mission control behavior. One easy thing I would suggest is going into System Preferences -> Mission Control and uncheck "Automatically rearrange Spaces based on most recent use," assuming that is checked. This may solve your problem, maybe not.

Screenshot of Mission Control Preferences

Solution 3 I'm a bit dubious about this one, but it's easy and worth a shot. Basically, you need to remove the Caches folder in your User Library folder. You can try to do this with finder, but I suggest opening terminal and entering

sudo rm -rf /Library/Caches/ColorSync
rm -rf ~/Library/Caches

And then restarting your computer. Please note that you may clear your user-specific caches with that second command, which include caches from other Applications and things like iCloud. These are caches, so you shouldn't experience any real data loss, but certainly be a bit cautious with this one.

I wish there was an easy fix. Hopefully the mission control solution works for you, but this seems like it's been a problem for several years.

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  • I've tried to use displayplacer, but it didn't fix the problem. I'll give Solution Two a try
    – bheussler
    Jul 20 '20 at 20:43
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In the Display Preferences, each monitor is listed as P24h-10 (1) and P24h-10 (2), and they can change.

The problem here has to do with the EDID information the monitor is send the computer. What's happening is that the monitor isn't sending "enough" identifying information that the system can find a unique value. Most of the time it's a serial number.

What is happening here is that the monitor is being detected and it's getting the model info from each, but everything is identical so you get the parenthetical number after the model to uniquely identify it - it's like what happens when you try to copy a file with an identical name into the same folder; you get file (1) and file (2). Which monitor goes where depends on which order they're detected.

It's like flipping coins - two identical monitors randomly being turned on; law of averages says you've got a 50/50 shot at things showing up the way you expect.

If you want to verify this (and you happen to have a spare monitor), plug in a different monitor and you'll see things stay the same.

It's not a bug or issue with macOS - it's just dealing with the lack of monitor identifying info as best it can. There is an app, however, called Stay that has been successful in solving this. See: Arrange different external displays of same model to different positions

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  • Does "Stay" work? It sounds like it's used for keeping window position on a display. But if what you're saying is true about the monitor's EDID information, then there is nothing preventing the monitors from changing arrangement.
    – bheussler
    Jul 20 '20 at 20:46
  • From what I understand, yes. I can't test, because the two Dell UltraSharps that I have actually send out proper EDID info to uniquely identify them. I know this problem is prevalent with LG monitors - big time! If Stay doesn't work, what you might want to do is when booting your computer, turn them on in sequence so they get detected in the order you want.
    – Allan
    Jul 20 '20 at 21:01
  • I was just doing a search and found this company that makes EDID emulators so you can go in and "intercept" the info and make sure the info your computer is getting is the info you want it to get: blackbox.com/en-us/support/support/resources/black-box-explains/… This is obviously overkill for your needs but there's obviously solutions for dealing with "crappy" EDID data the manufacturer puts in their monitors.
    – Allan
    Jul 20 '20 at 21:04
  • If I understand correctly, the best low tech solution would be to turn off one of the monitors before putting my Macbook in sleep. Then when I wake my computer the next day, turn the monitor on again.
    – bheussler
    Jul 20 '20 at 22:06
  • That might work. Give it a shot.
    – Allan
    Jul 20 '20 at 22:11

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