That crash was actually caused by DemonBuddy messing up, but try and update to Stash Replacer 1.9.8, it may help. Always keep your plugins up-to-date - I have been known to update my plugins twice a day at times (and other times, once every week or two, depending if it needs lots of changes or not!).
Does +XP gear stats roll on high-end items? I thought you couldn't get +XP on ilvl 60+ gear? I might be wrong.
Hopefully this should just be a rare circumstance. Can you check the logs, and search for the string "GSError". You'll find lots and most of them won't actually be missed loot - I have tried to word the lines very carefully, and if you look a few lines above an error that says "tried to interact with an item twice", you should see new logs I added in 1.9.8 saying it was already picked up - but if you have a good look through the logs from the point the item dropped to the ground, to the point the bot blatantly missed the item and is no longer fighting but just walking past ignoring it, see if you can find any log-entries referring to that item and paste them up for me (along with the few lines above and below).
Where abouts in the Act 2 town-run does it get stuck? Can you describe the order of events to me? Also look in the log-file for the string "GSDebug" - you should find log entries from my plugin saying which part of the town-run routine it is on, so you can tell where it got stuck. Please give me detailed information or I really can't help!
Also yes lag does cause a LOT of issues - but nothing anyone can do about that really

The way I cache all data before I start stashing/salvaging/selling items should reduce problems caused by lag though.