I just migrated from Groove. After the migration I have seen that couple of hundred of titels couldn't be moved. in the migration result all of them are from you OneDrive folder - local - and most of them ripped DVD's.
Reason is that Spotify could not move them as they were not on the Spotify catalogue. Why can I not simple still listen to my local music? When I connect my OneDrive to Spotfy under settings, I can't see 0 music titles despite of the fact that there are more an 300 in different folders.