My iMac crashes when it gets to sleep

My iMac crashes overnight - when I use the "jiggler" software (automatic mouse click every 2 min), it stopped crashing, indicating sleeping makes the Mac crashing (is it during iCloud or/and Time Machine updating? although both work fine when the sleep function is blocked with jiggler.

Before using jiggler, I tried safe mode, reinstall Catalina, recovery, NVRAM/PRAM reset, SMC reset, Hardware test (no problem detected), Disk Utility repair, -> all without any connection else than mouse, keyboard and ethernet. User switch. Nothing solved the problem.

Although jiggler solved the problem, I would still like to know from an Apple specialist what other problem could force me to block sleep to avoid constant crashes. Thanks.