New Mac mini: Monitor not waking up

I treated myself to a new Mac mini, to use at work instead of my MacBook Pro. I have two screens, a standard Samsung 24" monitor connected via HDMI, and a LG UltraFine 4K display, connected via USB C.

Both monitors work fine, but when the computer goes into sleep mode (or screensaver), only the Samsung will wake up. The LG 4K does not “wake up” until I unplug the USB C cable (at either end) and plug it back in again.

I never had this experience on my laptop, when connecting these same two monitors.

Does anyone have any suggestions? The LG firmware is up to date, and there doesn’t seem to be any other variables I can play with!

Does it stay totally asleep, or does the backlight come on and merely leave you with a black/blank screen?

Has this always happened? If so, maybe it’s cable-related. (I’ve found many monitor problems to have been bad-cable or cable-gone-bad issues.)

Is it configured as a 2nd monitor? FYI Apple recommends you should use the LG UltraFine 5K Display as a second monitor with Mac mini and Mac Pro because the display might not turn on until you boot into macOS. Perhaps it’s related to that?

Similar problem discussed here:

@RosemaryOrchard move this to tech support

thanks for this. I’ll bring in another USB C cable for tomorrow and see if that helps. so weird. and I can try switching the displays, although it would be a pain in the butt!

Update: I think you were right. It appears to be cable related. I bought an actual “thunderbolt” usb c cable and the problem seems to have gone away. It’s crazy that my old cable was good enough to work 97% of the time, but not to wake from sleep!