we have a custom script that suppose to add lot number to the item record upon completion on the work order, the lot number is generated fine but it doesn't go on the item record, and there is no error that comes up on saving. It only happens to few items and I don't see any visible difference between the two items for the one that it does and for the one that it doesn't any pointer to where i should look

Did you confirm those items were created as “Lot Numbered / Serial” items as their type ?

Yes it is lot numbered item, (Lot Numbered Assembly/Bill of Materials)

probably want to take a look at the lot number record

It create the lot numbers, just doesn’t put it on the item record and that too only for few items. It’s script return by partner, might need to involve them

lot number record has details about the lot, such as which item it applies to, its status, expiration date, and quantity information