Gleb Kolyadin is a member of Iamthemorning. He’s just released a self-titled debut album, which Roon correctly identified. The individual artist record for Gleb though does not appear to associate him with Iamthemorning.
However, when you click on the text-link for Gleb Kolyadin under the Iamthemorning artist summary text - it takes you to a different record for Gleb Kolyadin, which is then associated with the listed Iamthemorning albums (well, 2 of 3 anyway!)
I’ve tried to find a way to link / merge them (editing artist data for both so it’s identical) without success (I suspect that’s not something that I can do as an end-user anyway).