In another thread - Numbers in Genre Fields - I told that for some time now some fields tagged with Metadatics lead to some empty fields in MC.
I found the solution: the "Work" field in Metadatics was previously "grouping" in MC and now also "Work" in MC.
So I use the Move/ copy feature in MC the move the Data from the "grouping" field to the "work" field. As already written in the other thread my collection is huge - 253320 audio files (5,8 TB).
I suggested that it will need some time for the operation but didn't expect what happened: it's working for 14 hours up now to and more than 87000 files still are on the "copy" move.
Frank