Turns out it’s a bad record. Deeper into the BO.
BMM10_GD.FindFirstPartMtlSysRowID(String company, String partNum, String revisionNum, String altMethod, Int32 mtlSeq) in C:_Releases\ERP\RL10.2.600.0\Source\Server\Internal\BM\EngWBLib\BMM10-GD.i.Queries.cs:line 439
FindFirstPartMtlSysRowID was returning null
I can’t figure out why but once narrowed down, was able to undo checkout on it at least.