Do me a favor and open the epubs in question with some sort of zip archiving software. I don't mean you have to unzip it, just explore its contents with something like 7-Zip or the like. Focus especially filenames and any potential exact duplicates. Let me know what you find.
I ask because I've had similar issues opening validated epubs in a reading app (which is Adobe RMSDK-based). I've not been able to link it to Sigil specifically, but I've not been able to rule it out either.
Last edited by DiapDealer; 12-23-2015 at 01:12 PM.
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