Selling one item then mashing sell for the item that replaces it in the slot results in selling phantom copies. Attempting to take unique items back like weapons crate (and not through reseting sold items) results in a fatal error.
Have that as well. Selling, resetting or exiting the menu usually does not cause an error. If you avoid spamming the sell button, it shouldn't happen at all.
I made a bug report about this before, but I thought it happened, due to old and slow hardware. Do you experience any lag or heavy input delay? Are you using old hardware as well? It could help narrow down the problem.
Old hardware isn't the problem here, afaik. The game just lags when mass selling items now. Previous patches (specifically the ones before drake changed how things load) worked fine without lagging or anything of the sort on my end.