Unexpected User Exit Error (3), coming from QT_EU.Query Tree occurs when transacting a move order?

Hello, I was wondering if anyone has seen the following error before when conducting a transact move order (pick confirm)?

This was reported by a user but so far we have not been able to replicate the issue in any way.

"After entering the serial number in for item Z382660 I clicked 'Save' to take me back to the first screen of the 'Transact Move Order'. I then ticked both items to transact them together and the below warning message appeared."

Would appreciate if understanding why this seems to happen occasionally.

Thanks,

Ian