I guess nobody knows the answer to my question, but in my font I changed all my discretionary ligature lookups to standard lig lookups, and now everything works okay. That's rather weird, I could've sworn that other discretionary ligs that I'd created myself in other fonts did show up just fine -- but perhaps I'm mistaken about that.
In any case, is this others' experience, too -- that only standard ligs show up as they're supposed to in ebooks, but not discretionary ones?
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