Must be a problem with the clients not asking the relay for notes, I guess.
Amethyst shows 0 received notes for that relay.
Discussion
The Iris.to client has this useful feature where you can "resend to relays".
Since Iris could load the notes from the Snort relay, I could resend it to all others. Now this specific note is not imprisoned by the Snort relay anymore.
Hopefully the Snort client will send future notes to other relays, too...