What is the MDM Version? Have you flipped the Consolidation indicator of the records to 2.
The Error snippet points towards missing Target ROWID OBJECT , so check if the target record is present in BO, if not, then probably it got merged into another record.
Also below this exception, there would be an additional caused by clause which would give you the actual sense of the error. Please share that
Are you giving a valid ROWID_MATCH_RULE which should be a Autorule per Hub as well.
Instead if not worried about Hub rules, simply populate as MULTI_MERGE and then run automerge job
Have you tried merging these records from the IDD application UI.