Somehow managed to lose two chapters. I’d slid them to the end of the MS, to keep them to one side for later, and I must have accidentally deleted them. My own fault, and there’s probably a way to locate them, but I don’t know how.
Ah well, it’s not an often mistake, and I don’t intend to repeat it, so lesson learned.
*I remembered I’d saved a copy, so all is well.