ToC Creation Problems

[ThanosNaranja]

I have a manuscript in Word 2013.docx form for input that always gave me a valid ToC whenever I generated a new epub from it. Somewhere around Calibre v5.0 I started having issues with my conversion appearing as corrupted by various eReaders (FBreader, Cool, ERA). The conversion always opened in Calibre reader, hardly ever in FBreader and sometimes in Cool or ERA. The performance was erratic. Usually, I found the related issue and fixed it. Then I discovered the 'e3' epub version spec and using it made a lot of my old issues go away. Epubs always showed as valid entries is the browsers of various reader apps and opened the way they were supposed to, but now they have no ToC. You can go to the ToC manually and use with it no problem, it just doesn't show up in the Reader menu.
So now I have v.3 epubs whose ToC's appear in some Readers and not others and I have to assume by process of elimination that the problem is related to how the individual Readers handle the Toc Pointer. Has anyone else seen anything like this?