for sake of clarity: alpha last but three version, namely 0c1f6881 (Dec 2021, 20th) never looses root, all is working as expected in same system (except Zygisk...)
something has been added that breaks something else
Good to know. In fact, I still keep that Alpha apk and my corresponding patched boot.img (just in case)
I have updated through all the later Alpha versions, updated LSPosed, HMA, installed and updated Shamiko
Sometime among those updates I started to observe instabilities. I never observed loosing the root but occasionally it loop-boots two or three times (soft- rebooting) before booting successfully. One day it rebooted five times to TWRP (I didn't do anything there except wiping Cache and Dalwik trying to 'help') until it finally rebooted successfully to the system
Since it does not happen on every reboot and since (as mentioned above) I updated various components, I was unable to point to anything specific (Alpha, Shamiko...) but my hunch was that it's maybe related to Magisk (thinking that I saw it first time upon updating Alpha from that version, before all the later updates)
But without a hard proof I didn't want to charge anything or anybody