Primary Text Frame auto flow does strange things
Auto text-flow suddenly produces this result while auto-adding new pages to fit the text-length.
Maybe it wants me to produce more "experimental books"… who knows.
Bob K commented
I would title my problem the same. ID 2019 in Mojave. in a 140 page text book, one or both of the text boxes on facing pages suddenly became a tiny box in the centre of the spread. It looked like the text had disappeared until I investigated the tiny dots in the centre of the spread. Those turned out to be my text boxes - shrunken and moved...