The cause for it was that this artist was merged into another artist, and the neighborhood code in ListenBrainz did not redirect to the merged entity.
If you open SOFT PLAY - MusicBrainz and take note of the ID in the URL bar, you’ll notice that you get redirected from f7a98893-… (the artist that was merged) to e33c7d5a-… (the artist that it was merged into).