I have quite a few epubs I purchased from Fictionwise back in the day. From time to time I pull one out of my backup and load it into Sigil so that I can cleanup the many, many problems with it. Before 2.3.0 it was a workable thing but now Sigil crashes when I open one.
Ironically, I can open them in Caliber but I really don't want to go that route.
My preferences are set to mend not well formed html source code on open.
Here's an example if you have time to dig into it.
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Removed Coprighted (1994) book. Do not post copyrighted material.