as @IRobertI mentioned and you described, it's a configuration mismatch with print core 2.
As your problem and solution both happen in Cura, I assume that you didn't tell Cura that print core 2 has been changed to "BB".
Is your UM3 connected to Cura by LAN or WIFI? If yes, you easily can syncronize the actual setting of the printer to Cura. If not, you must select the print core manually, the same way you told Cura which material is used.
If you have inserted a "BB"-core into the printer, but it tells it's "AA", you should refer to the following thread:
Are you using an AA-core or a BB-core? PVA requires a BB-core, one was included in the box when you bought the printer if you bought it new.
Link to post
Share on other sites