I'll try with update newly downloaded Nikgaps next timeAre you installing an up-to-date NikGapps package? If not, try one - https://sourceforge.net/projects/nikgapps/files/Releases/NikGapps-R/04-Jul-2021/
Edit: I've re-read your post. I've missed where you said that you have to do a factory reset, and it will boot with that same NikGapps package. Hmm... I'm not sure at all. I personally reinstall Nanodroid MicroG and Magisk after updating to a new build, and never have issues with bootlooping.