I have the same album. In Roon, it is complete - all artists are showing for all songs. My files are FLAC, and I do have the artist tags filled in for every song. I notice Roon identifies the album with “Greenpeace: Rainbow Warriors [#1]” on AllMusic. Not sure why it has “[#1]”, but all the artists names are there as well. Maybe you just have to identify your album manually with this one on AllMusic.
PS… Thanks for mentioning this one. Used to be one of my favourite compilations and I bought it when it was first released, but I have not played it for a long time. Will have a listen to it now. 