Hello - have used mirror margins for years, no problem. Have tried restarting Word, does not fix it.
The first page of the book--Page 1--is treated like it is a left page (even, not odd), with the wider margin on the right side, rather than left. The margins are otherwise correct, merely reversed.
The issue is jumbled with some pages correct and for example two "odd" or two "even" in a row. Is a mess.
How to fix this? It appears maybe the book formatting codes have been mangled in some way.