FL to 20.5.1 (from I believe 20.1) I've had some serious audio buffer issues. I'm using a focusrite scarlett 2i2 sound card and a custom built desktop with very high specs.
I've updated all the drivers on my soundcard ...
FLStudio 20.5
PreSonus Audiobox USB96 interface
Various plugins (FlStudio, Klanghelm, Soundtoys, U-He, Sonalksis)
With my 2011 Macbook Pro i never had this issue. I don't have this issue when i'm using another program like Reaper ...