Stock recovery constant error, downgraded ROM and updates won't show

Hey y'all, I was on 2.19.40.22 rooted with one click root and successfully applied last week's update to 2.20.40.58 and kept root.
I tried to update to 2.20.40.59 and my phone got all sorts of ****ed up. So I successfully formatted and wiped everything and downgraded to pre-rooted 2.19.40.18 (also downgraded boot/droidboot/stock recovery). After unrooting SuperSU so I'd have a fully stock ROM, I tried updating. That got botched.

So I wiped everything again (including internal storage/data) and fully installed 2.19.40.22 and now my phone sees no updates from ASUS pending and every time I try to enter stock recovery, it just plays like it's trying to apply an update and then throws up the error message. This happens without any OTA update zips in internal storage to trigger recovery to try to apply an update.

I've also tried the other manual way to update (the method other than MOFD_SDUPDATE) and my phone will try to apply the update then displays the same error message again.

I'm at the my wits end having tried everything I can think of, have spent the better part of 6hrs ****ing with my phone. Anyone have any insight?