Invalid item source on line 5 Not sure what to do with this, as bom only has 4 lines nothing is inactive

First guess is an inactive item on the BOM, it may not even display on the BOM record itself.

How do I know if it doesn’t display on bom? When I deleted the work order and start again it worked so it comes sporadically

Maybe try a saved search or SuiteQL querying the BomReviaionComponentMember table