I’ve been fighting this battle for about 6 months now and am at the end of my rope.
I have read very video on Indesign CC to epub and cannot figure out what I am doing wrong.
My document has about 35 glossary terms and about 65 url hyperlinks throughout the book. I think they are the culprit but they have to be in there.
With the glossary terms, I was trying to link the term within the body copy (source) to the glossary term definition (destination) in the back of the book. THEN, I tried to reroute the glossary term word from the defined list (source) back to the page (destination) within the chapter that it came from. Can that even be done? (It works fine when I do it in Indesign but then messes up the validation in the epub.)
On one book I created valid hyperlinks from a list of illustrations to illustrations throughout the book. I didn’t need to create a link from the illustration itself back to the list though. So I didn’t quite do what you are trying to do.
It would seem to me that you could try to create a separate index (the function of which I have not used yet) where the glossary terms then can point to their use in the book. In fact, what if a glossary term appears more than once? What would you even do? Isn’t that where an index comes in?
Another thought on glossary items: create them as footnotes. If I’m not mistaken, InDesign turns footnotes into “pop-ups” so that people can read them without having to actually jump to a different page (when the ereader supports that).
But if you want to do it as hyperlinks, that should be doable (either with hyperlinks or cross-references in InDesign). What error are you getting?