Hi, yes we spoke about this before - Question About Musician Credits and I’m trying to fix this.
But unless you have evidence to the contrary I think your analysis is not quite right. The problem is simply that for FLAC that SongKong adds musicians to the PERFORMER field, and Roon treats PERFORMER as primary artist, If instead I add to INVOLVEDPEOPLE instead it appears okay.
I would like to add musicians to MUSICIANCREDITS but AFAIK this field is not understood for Flac only ID3 (as TMCL frame), or have I missed that ?