Seems possible if Groove was updated with some new DMR (digital media rights) protections/restrictions.
I found this article that says Groove is being replaced by Media Player during updates on some Win10 systems. Maybe yours has been updated/replaced? If so, it's likely Groove will no longer...
Can't be much help, but I have Win10 and Groove and it seems to work OK for me for playing mp3's. I don't use Groove much, I usually just use iTunes.
Have any of your settings changed regarding where Groove looks for music files?