(FIXED) CDR stopped working, all fixes here have not helped

UPDATE: actually, just fixed it. Copied the oldest backup of cdr_mysql.conf I could find back over the config file and suddenly it worked again.

So please ignore.

My Call Details Reports from the FreePBX Gui have stopped working.
The logfiles are still being generated in /var/log/asterisk, and I have tried
all the various suggestions made in variouls threads here (username/password
in /etc/asterisk/cdr_mysql.conf, permissions on session directory, GRANT permission
for Mysql user, etc, etc.

Can someone give me a clue where to start looking to track what is and isn’t happening?

If I cannot get this fixed, can I do a fresh install and then restore a backup?