I've had "strange occurrences' with page numbers, too but not exactly the same problem you describe.
I have come to the conclusion that editing page numbers can occasionally create a corruption on one page of the book that can be eliminated only by deleting the corrupted page.
First make a duplicate of your book for future reference by right-clicking on the book-name in the Collections page of the Book Module.
Then - in your original book - delete the page that is incorrectly numbered.
Then recreate the page from scratch using the corresponding page in the duplicate as your plan for the layout.
To avoid such mishaps I do the page numbering as the last step in creating a book.
Note: The corruption does not necessarily "sit" on the page with the wrong number. It could "sit" on any page of the book.
If deleting the page with the wrong number does not help, you have to go through your pages one-by-one in this way:
After creating your duplicate book delete page 1 of your original. If this does allow you to number the pages correctly the corruption was on page 1.
If you cannot number correctly re-insert page 1 by pressing Ctrl / Cmd. + Z repeatedly until the page appears again.
Then delete page 2 and continue as with page 1; and so on through the whole book until you have deleted the corrupted page. You'll know this because you can number correctly when the corrupted page has been deleted.
Tedious, yes. But it's the only way I've found. I just hope you don't have 240 pages.
Thank you, web-weaver. Your first solution worked very well for me. I checked all the subsequent pages and the corruption in page numbers did not simply move along.
I appreciate your suggestion of adding page numbers as the last step. I think that's wise.