External display blacks out temporarily when high CPU usage

Hi all,

I have been the most annoying issue with my external monitor. I’ve been trying to find a solution for months now, but nothing seems to work.

Whenever my CPU usage goes up, say I’m compiling something or watching videos, my external display (Dell 27 USB-C Monitor - P2720DC) starts blacking out for one-two seconds at a time and then comes back on. It seems to be that the busier the CPU, the more frequently it happens.

My GPU is Intel Corporation Skylake GT2 [HD Graphics 520]. I experience it both on Xorg and Wayland (currently running River wm on wayland). The same monitor, with the same HDMI cable, works perfectly fine on Fedora 34 on my work laptop. On Manjaro, I tried running it on the following kernels: 5.4, 5.10, and 5.12 (currently on the last one). I tried reinstalling the drivers.

The same laptop used to work fine with another monitor, but that one was connected to VGA. The new laptop doesn’t have it, though, HDMI is the only connector that’s common between the laptop (System76 Lemur 6) and the monitor.

I’d appreciate if anyone has any ideas for what else I could do to try and fix it, or what I can do to debug it.