SUMMARY

I've tried this with multiple source engine 1 games (TF2, HL2, Portal 2), and all exhibit the same behavior, however this is not observed with other games such as cities skylines or KSP (Unity engine).

After launching one of the effected games and playing for a bit, all is smooth. However as soon as the game exits, window dragging and animations are at around 5-10fps. This problem gets worse and worse the more you open and close the effected games. Halting the compositor (ALT+SHIFT+F12) makes the problem go away, however re-enabling the compositor makes everything sluggish once again.

Unticking "Allow applications to block compositing" has no effect on this. Weather its enabled or not, as soon as the game exists a noticeable slow-down is observed.

It should be noted however that during these slow-downs, 3D applications are unaffected (I can re-launch a game whilst having slowdowns and the games are unaffected).

STEPS TO REPRODUCE
1. Open a source engine game
2. Play for a bit, then close it
3. Drag some windows around, it will be far more sluggish than before


OBSERVED RESULT
After the game is closed, the compositor is noticeably slower than prior to launching the game. Repeating steps 1-3 keeps making the compositor slower until the entire system is unusable.

EXPECTED RESULT

Compositor should not drastically slow down after closing a game.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux (5.12.13 kernel)
KDE Plasma Version: 5.22.2
KDE Frameworks Version: 5.83.0
Qt Version: 5.15.2

SYSTEM INFO:
Razer blade 2018 (i78750HQ + GTX1060)
NVIDIA driver version: 470.42.01