I noticed i had two artist objects with same name for what should have been 1 single artist.
They had different mbzids in "edit metadata" (there were no ids embedded in id3 tags) - so that made sense (in correct identification)
I ran a re-identify against 2nd object using mbzid of 1st object, expecting the 2nd artist and its content to be merged with 1st.
instead i ended up with still 2 objects both with same mbzid.
mbzid is a unique primary key for an aritst, so i dont think it should be possible to have two artists with the same mbzid?
FWIW removing the content of the 2nd object and re adding to library sorted everything out.