Since I updated from Sierra to High Sierra I have an issue when i connect a second monitor to my macbook pro 15 inch 2017 (USB-C to HDMI -> HDMI to VGA). Namely, the OS starts lagging about every 5 seconds which makes it impossible to work with it.


The issue does not occur when booting in safe mode. I tried resetting NVRAM and SMC.

Any suggestions?

  • Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. – IconDaemon Nov 20 '17 at 12:19
  • It is possible there is a glitch when using two adaptors connected together. There exist USB-C > VGA converters in the wild. Perhaps you can capture one and give it a try. These adaptors work best at my institution. We tried a few 3rd party adaptors, but these won out for compatibility and durability. – IconDaemon Nov 20 '17 at 12:22
  • Doest "the OS starts lagging about every 5 seconds" not sound like a specific problem? To state the obvious, I would like a fix for this specific problem. – Jeremy Knees Nov 20 '17 at 12:24
  • I understand what you wrote, but there's not enough to work with to give you a concrete answer. You give a link to a Apple forum post that has a tenuous connection to the problem you are experiencing. There's just not enough information about what you've done to correct the problem. To augment my post, I have had painful experiences with computers and monitors connected through multiple adaptors, where a single adaptor solved the problem immediately. Q: When you detach the 2nd monitor and adaptors, does the computer work correctly without the lag? I've retracted the Close flag. – IconDaemon Nov 20 '17 at 12:31
  • "When you detach the 2nd monitor and adaptors, does the computer work correctly without the lag?" - Yes – Jeremy Knees Nov 20 '17 at 12:32

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