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my guess is that the php 7.0 was the solution.

#1 - i agree with regards to backups. leave the system as is.
#2 - catalog side works fine.... admin side does not. to turn on debugging for the admin, change this file as follows:
...

have you turned on debug as well as error reporting? will hopefully point to the exact problem....

with regards to the code history as well as "blame", my PR was to help with debugging problems,...