Tnx Toufiq, it worked partially. I have installed the provided backup.
The problem I have now is: you provided me with the bckup version from our dev-site, and not from the live site. Hence I can not reuse your bckup, because it does not contain all the content changes the client did the day before the update to SPPB 5.5.2 on the live sit.e
Can you please tell me what needs be done on the live site to get rid of the error Cannot read properties of undefined (reading 'data').
I already stated, that the client is adamant of not running over the current live site version, since a whole lot of content changes would be lost. So it is not an option.
Best Ivana