For the past month, my weekly jams playlist has been pretty much nothing but one artist.
See for example this latest one: https://listenbrainz.org/playlist/ba6e3f5d-3b11-4f53-9489-5af7f54eb1c6/

The daily jams playlists however are working fine.

I looked at the raw recommendations and while I do have to go to page9+ to see more variety, the variety is there.

Mayhem suspects that a step in the playlist creation hasn't been applied: limiting the number of times each artist can appear in a playlist.