The late 2020 M1 MacBook Pro does not seem to be playing well with the LG UltraWide 38WK95C 38-inch external display directly connected with a USB-C cable. The display blacks out (as if the cable physically disconnects) every hour or so. The issue usually resolves itself within a few seconds but sometimes I have to restart the computer to get it in a good state. The problem occurs with both USD-C ports and does not exist with the late 2016 MacBook Pro.

How can I diagnose and fix this external display issue?

  • Which cable are you using? My 4K belkin ones are working very well so far.
    – bmike
    Nov 23, 2020 at 18:48
  • Same cable for both MacBooks? The other option is to try a different monitor Get and use DisplayPort input and boot HDMI to match the LG as close as possible. If the issue persists, you might have a problem with the Mac itself warranting further diagnosis
    – Allan
    Nov 23, 2020 at 19:58
  • @Allan: Yes, same cable for both MacBooks.
    – Randomblue
    Nov 23, 2020 at 21:30
  • @bmike: It's the cable that came with the LG external display.
    – Randomblue
    Nov 23, 2020 at 21:30
  • 1
    I would swap it out with a new one - you need a spare eventually and I’ve seen vendor cables be less reliable than the Belkin ones. We probably replace one in 20 of the LG over the first year and less than 1 in 100 of the Belkin.
    – bmike
    Nov 23, 2020 at 21:37

1 Answer 1


The problem seems to have gone away after updating macOS Big Sur from 11.0.1 to 11.1.

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