Are you sure this isn't just https://github.com/ValveSoftware/steam-for-linux/issues/11446?
Yeah, looks very similar. I'll have to try the LD_PRELOAD="" workaround.
Hello @TrueNeutralDesu, as @Saancreed noted, this issue is already being tracked at https://github.com/ValveSoftware/steam-for-linux/issues/11446. If that workaround doesn't affect how the game behaves, then please add a note to the older compatibility report for the game at #58 and we can continue to ponder it over there.
Closing as a duplicate.
Compatibility Report
System Information
I confirm:
steam-238960.tar.gz
Symptoms
After about 30 minutes of playing Path of Exile game starts stuttering. Ingame graph shows CPU related lag going from about 5ms to about 55ms. This doesn't happen when playing on standalone client, however if you add standalone client as non-Steam game and launch it from Steam then stuttering also occurs after half an hour of playtime. Changing any options in game as well as Proton versions does nothing to help the issue. Only way to get rid of it is to restart a game.
I added logfile (compressed since it was 60Mb) but the relevant lines seems to be:
Haven't found anything related directly to this issue online. Problem is present for a few days now.
Reproduction
Any time game is played for more then 30 minutes.