USB devices not detected, LG Ultrafine 5K

I have a keyboard and DVD drive connected to the USB ports on my LG Ultrafine 5K display, then the display is connected to my 2020 Intel MacBook Pro via Thunderbolt.

Occasionally, when I plug in the MBP into the monitor, the monitor comes on but none of the USB devices work. The LG’s built-in webcam will also not work, I presume it’s on the same USB bus as everything else.

When I reboot, everything works fine. I’ve tried an SMC reset several times, eventually the problem comes back again. Has anyone else noticed this behavior?

I see the same thing (although with LG 4K, but also with the CalDigit dock. Also a 2020 Intel MBP). Something messes up the thunderbolt controller, but only one side. So my typical fix is to plug it into the other side. Seems to be less of a problem (maybe gone?) since updating to Big Sur, but hard to really tell since I reboot often enough to get into bootcamp that it is hard to track. I.e. I typically reboot every day or so, which is also about as often as I unplug from my desk, so the problem clears up. If you do ever end up working with apple, I found that a documentable approach to get something to submit is to do a system report (apple → about this Mac → system report) and if you go to the thunderbolt portion the controller that is dead won’t have the same amount of info as the working one. I.e. instead of having the ports it’ll just be the first few lines of detail. Might help apple diagnose. I’ll try to keep an eye out for it happening again on days when I don’t use bootcamp to see if it is still happening for me.

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Good idea on the system report, I’ll be sure to check that the next time. The support person I’m working with just had me do a Big Sur upgrade, so I guess we’ll see if that does anything. So far the only change is everything got slower compared to Catalina :see_no_evil:.

Do you ever have yours reboot when you plug it in?

I don’t think so, typically it’ll panic when sleeping, plugging in doesn’t seem to trigger it.

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I haven’t needed windows this week, so good test to see if the problem is still showing up for me in Big Sur, and it seems fixed. Haven’t had the thunderbolt not recognize USB devices all week with lots of plug/unplug cycles.