[stumped]

i am so fed up of seeing this when I open a book in sigil

and it returns EVERY TIME i use modify :e.g. i fix it with "mend & prettify" and test that it opens with no errors, but then re run modify epub on the book, open it again and its back!

very few options ticked in modify epub ::just fix spans, cover, TOC, update metadata. and anyway , running it a 2nd time without doing anything other than mend and prettify should give it nothing to modify?
yet somehow it reintroduces this error, every single time

so easy to prove
open book in sigil - no error
close book
run modify epub
open book in sigil - error is back

someone please tell me how to break the cycle