I had the same problem, solved it here:Hi there,
I tried to do the same, also coming from 8.8.30 on MI 8, but didnt work;
The phone cannot boot on system and will reboot on TWRP.
I have installed the latest TWRP (yours) and cleaned cache / dalvik.
I am reverting to 8.8.30 (thx god I was able to revert).
I guess full format is still necessary, how did you manage ?