Addendum:
I forgot to mention that Ancestris is now loading my GEDCOM (older backup from 2022-03-17) very slowly again. The sources and source locations are back.
From 81% it takes forever. I think the data structure of the sources and source locations is pretty jagged!
But I didn't create any of those myself.
Almost all of them were created through multiple GEDCOM imports.
From maybe 30 - 40 different sources (software programs (a-z), for Windows, Linux, Mac, Ancestris, MyHeritage, ...)
Ancestris shows me some messages, which I unfortunately don't (directly) understand (I don't speak the English language - and our German translator seems to be a phantom).
.Empty lines found, 'invalid' tags, unassigned, and so on.
So before I really go any further and then try Ancestris under 'normal' conditions, I have to clean up my GEDCOM first!