hmm.. I would remove them all.
and then add one. That I KNEW worked. test the index.
then repeat with stuff I was "less sure off"
perhaps a "newly" added title cause the failure? Total and utter guesswork.
It's always easier/better to work from a known set of variables.
remove calibre from the equation.
Do the titles get listed in things like
HACKED UP READER?
that
might indicate that in fact it is your system/indexes that got corrupted
somehow
I am no expert in this area. but if feels like mangled indexing.
Using a 3rd party app that DOESNT rely in Amazons Indexing could confirm that.
hope that helps.
I note that
https://www.mobileread.com/forums/sho...8&postcount=51 there appears to be a lot of noise about the latest indexer not being super solid.