A dindex whose associated dblock is missing is pretty useless, so can probably just be deleted.
If the missing dblock was a problem, I think list-broken-files would have flagged it as such.
If you want to test, you could either move the dindex or rename it to not begin with duplicati-.
That just hides it while keeping it around (just in case). A smooth DB recreation would be good.
Smooth would stop at 70% on the progress bar. Not-smooth would be past 90% and quite slow.
This was touched on earlier in terms of volume. Past 70% gets into downloading larger dblocks.
Remote file referenced … but not found in list, registering a missing remote file #4586
is an issue with similar symptom that was found by DB recreate for a restore without database.
Possibly yours has similar origins, but neither case has enough history saved for good tracking.