Thanks Erik,
I discovered that the filter box appeared just after posting the note, when I created a rolegroup.
As far as I can tell the two versions match now. Thanks for pointing out the dynamics.
Uncertainty keeps us on our toes and challenges us!
It's a matter of confidence, or lack of it, both in the product and in ourselves. The upgraded site created several days of work and worry when the file sync error appeared.
Restoring from backup is going backwards and only delays going forwards again. Only really good if we've really lost it. Finding the cause and its fix is progress!
With the filesync issue switching off the scheduler permits the site to work, but may only be masking weaknesses.
If it's broken, can it be mended? Is it more economic to mend or replace?
A clean install may still have the potential to break. The problem may be latent in the earlier version, so restoring from backup may not help.
Various sources advocate backing up before upgrading. Surely a must. One step further and backup each significant portion of work.
Some say test the backup and upgrade on a localhost. Great, but it's a different environment which may not show up problems, especially ones to do with permissions, so we can't rely on it.
Gouda cheese, on the other hand, is quite different. When it looks good on the outside and smells right, we can rely on it tasting great.