It was noticed that, when using a heavy application, as a game, after some time GPU hangs will start to happen. They happen constantly and, if nothing is done, they never stop. The system is recoverable as the user can access a TTY and kill the offending application (after waiting a few minutes to start the TTY).
After that, graphical demanding applications either run slower (it's not just the product of the lower frequency, it's different) or start causing the GPU hangs again. Restarting the applications that didn't cause GPU hangs will make them work normally again.
This started to happen after the security fixes to Intel GPUs. Power management is also disabled. It was noticed drm-tip does not have this bug.
ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.4.0-12-generic 5.4.0-12.15
ProcVersionSignature: Ubuntu 5.4.0-12.15-generic 5.4.8
Uname: Linux 5.4.0-12-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu16
Architecture: amd64
CurrentDesktop: XFCE
Date: Sat Feb 1 22:06:22 2020
InstallationDate: Installed on 2017-06-13 (963 days ago)
InstallationMedia: Xubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
SourcePackage: linux-signed-5.4
UpgradeStatus: Upgraded to focal on 2019-12-22 (41 days ago)
mtime.conffile..etc.apport.crashdb.conf: 2019-08-29T08:39:36.787240
As asked on #ubuntu+1 IRC, I tested on Xubuntu Focal Daily Live. It was needed 2 hours until I got a GPU hang, but once got it, the computer behaved exactly the same.