Was there sufficient space on the page for the caption, at least one full body row (ID will not split a row if the cells are deep) and any header rows, AND the footnote? In the Keep Option, was it set to keep with more than one line (a table would be considered a single line, I think, for keeps, so even if there's room for part of the table, you might need room for all of it), was it also set to keep with previous, or the previous paragraph set to keep with next?
Keep options can easily cause oversets when there is no way to resolve a conflict in the rules.
Yes, there was sufficient space for several rows, as far as I can see. At least, in the result after I solved the problem (now by making a paragraph override not keeping the table heading together with the next line) there are several lines plus the footnote. The keep option was set to one line, and not to keep with the previous line.
So, in combination with a table breaking over pages, keep with next is no problem, and footnote is no problem, but combined, there is a problem.
Even when there wouldn't be enough place left on the page, you would expect Indesign to just move header, footnote and table to the next page. They all were on the same page before I started shifting text (by chance). By the way, the table only just didn't have to break then.
I've just done so. Thanks for your time.