Is there a hog process using all the CPU? (Ostensibly at a higher priority.)
First thing I check for on my multiuser systems. Especially when 500+ users “pause” and dozens generate a “Service Now” ticket flagged as an “Incident” and dozens of phone calls.
I imagine process management is somewhat primitive on single-user systems even versus an old 30 year multi-user system. (You can’t just get 500 users to do a control-Y, there have to be “tools”.)