There's a few reasons it can miss items atm, and not a complete list but some things;
- Random DB burp (it happens in various places, from failing to read an item, to failing to "Interact" with one to pick it up).
- Item not within current "loot-radius" at a point in time that DB is not busy moving/fighting.
- Frozen/rooted right at the end of combat, and so stash replacer blacklists an item thinking you can't reach it rather than wait for you to get unrooted (something I can probably fix in a future update).
I wouldn't worry too much about it - if anything, those rare misses could well just be the stash replacer over-riding a situation where default Db would have crashed/failed/got stuck in a loop, there's all sorts of "safeties" throughout the plugin that check for memory mis-reads and item-handle-failings etc. and instead of crashing or getting stuck, it cleanly either blacklists the item and continues, or tries to do a town-run to see if it can fix itself.
I'm using .199 and 1.9.3 and I have seen it ignoring 60-63 rare rings even if the bot circles away it comes back to pick up the other rares + blues, but leaves ring behind this has happened like 4-5 times when I have been on computer.. Maby it gets blacklisted or something I don't know seems to pick up other items perfectly fine