In my customer environment, there are a couple of new parts that they have created.

Now when we want to execute Returns on the MWO, it suddenly asks for a Lot Batch no:
 

Whilst the Lot Tracking for that part is not enabled:

Now during prototype we had set up a different part to show case, which has a similar set-up to the part above:
 

and for this one, MWO doesn't ask for a Lot Batch No.

Here my returns work as intended and designed.

Also in the inventory part records, there are no differences to be detected, other than the on hand quantity. This is shouldn't be an issue, seeing as the returned parts are Serial Object that are part of a structure. There are a couple of differences in the structure/serial objects such as customer vs company owned, objects that have been created via the service object screen vs functional & serial object screens, but they don't solve the issues that we are having, already tested those differences.

The other issue we are encountering is when a return has been added (either via planned lines or quick returns/add functionality), is that we cannot see a list of available serial numbers, whereas with the other part number we can:

I have tried basically everything, but cannot figure out why MWO decides to ask for a lot batch no suddenly, whilst the set-up is matching the prototype part no.

Can someone help me ?

Thank you!