Try
update_KUALBooklet_hotfix_v2.7.22_install.bin from the
KUAL-v2.7.22-g699ae4a-20191115.tar.xz archive in the snapshots thread:
https://www.mobileread.com/forums/sh...d.php?t=225030
Drop that in the root of the USB storage and then:
Menu > Settings > Menu > Update your Kindle
Not sure if that will install on 5.12.3.
Failing that:
;log mrpi should function now.