text skipping text frames
InDesign CC 2020 15.1.2
macOS Mojave 10.14.6
I've been working on a text-only file, with lots of footnotes, one text frame per page, and everything working smoothly.
Now suddenly the story skips one or several text frames/pages on continues later, randomly causing blank pages:

Has anybody an idea why this is happening? The usual suspects – Keep Options in paragraph styles, No Break in character styles – do not seem to be relevant here (only Keep Options are applied, and correctly).
