This happens for the Dutch unused images as well like [https://nl.wikipedia.org/wiki/Wikipedia:Wikiproject/Erfgoed/Nederlandse_Erfgoed_Inventarisatie/Ongebruikte_foto%27s_van_gemeentelijke_monumenten this page]. This happens at around April 7 2023. On April 3 it still was OK As resolved images stay on the page, I think the harvesting from the heritage lists fails. The indication of an error at column 'descr_nl' might point to a Dutch description. Maybe one of the Dutch desciptions is too long. The template involved might be nl:template:Tabelrij gemeentelijk monument . ~~~~

This particular example is now OK, after T316236 "Reload WCQS from dumps has performed" has updated data on several hosts, last Tuesday, Oct 25

I also have had many of these errors. I sometimes work for hours with the same session, and I agree it might be time-outs.
In my experience: I can continue right away if I open a new browser session.

I also found this bug. and reported it as T313185

Here a query of the 40 witches, with as much of details I could find