Player-created vibrations stop being retransmitted by amethyst when the player switches into spectator mode

Create a loop of skulk sensors and amethyst blocks that a vibration can travel around infinitely. Place a trapdoor a few blocks away to start the loop, then set your gamemode to spectator, and the vibration disappears. (Specifically, it continues on its path to the next sculk sensor, but it is not retransmitted out of the adjacent amethyst block.)

If you instead trigger the trapdoor with redstone, that vibration will be immune and will continue around the loop when your gamemode changes. I believe vibrations store a “player-created” variable to determine whether they should trigger sculk shriekers, and it is only the player-created vibrations that have the bug.