I recently upgraded to 5.4.0-37 kernel and it keeps freezing when I leave the computer idle for some time.
I'm using Ubuntu 20.04LTS.

I booted on 5.4.0-33 (previous version) and it works without any problem.
There are no logs regarding the freeze. No dumps, no panics. It freezes the entire system and I can only reboot.

AMD Ryzen 7 1800X
32GB RAM (two sticks: Part number KHX2666C16/16G)
Asus PRIME A320M-K
AMD Radeon R9 390X 8GB
NVMe SSD 512GB (I don't recall the brand)

I tried radeon and amdgpu drivers, since the video card is supported by both, but the issue still appears. The only consistent way to fix it and break it again is by changing the kernel version, so the only way to make the system stable again is to boot into 5.4.0-33.
The freeze only happens when I leave the PC untouched for a couple of minutes and the power management kicks in to try to turn of the monitor. It does not succeed though, as I always walk back to an unresponsive desktop, sometimes with a black scren, sometimes with a screen that was in the middle of dimming to black, and other times completely turned on (or maybe it was fading back to black and hanged sooner. I have no way of telling).

I tried to disable power management from the screen saver settings, and it still freezes when it tries to quickly power down the monitor.

I haven't found any way to debug this, since there is not a single log about any kernel panic or anything related.