Comment 4 for bug 1677383

Are you sure you checked both test epubs? I included 2 samples for the reason that one had text and the other didn't.

The main <dc:identifier> for test2_scrambled.epub is:
<dc:identifier id="uid" opf:scheme="ISBN">9780091799878</dc:identifier>

It may be invalid for other reasons but not because it has no text.

If there is no calibre library ISBN for the book (which was the case in my library at the time I first encountered the problem) then Embed Metadata still results in the 'OPF has no unique identifier' error.