When using the inventory tool, Koha attempts to write a date and time into the datelastseen field. Since that's a date field, the update fails and the item ends up with 0000-00-00 for the date.
This may be a red herring. I thought I saw this behavior on a library's site but have been unable to recreate thus far.
Still fighting with this, but running theory is it fails in the afternoon if one is using 12-hour time.
I've been able to recreate this behavior on 20.05, but only in the afternoon :) To recreate: - Set TimeFormat to 12 Hour - make sure cataloging log is on - wait until afternoon - have an item with barcode "TEST" and callnumber "9999" - in Inventory, upload a text file of just the barcode "TEST," limit inventory to callnumber range 9999-9999 - submit inventory, it tells you it set Date Last Seen to today for 1 item - go to item, confirm it shows a null Date Last Seen - look at the modification log, see Koha tried to put a date and time into Date Last Seen
I've tried to replicate the issue on master, but it all seemed to work alright.