Packet decoding error on join

[pepperoni21]

Hey, I tried this proxy with a 1.20.1 Paper server and I got this error when I connected:
Connection to 127.0.0.1:39048 ended with: failed to decode field `on_ground` in `UpdateEntityPositionAndRotation`: decoded boolean is not 0 or 1

I use the default config. For the first error message (in 1.20.1), I can see the connection in the paper logs:

lobby-mc-1  | [16:26:38 INFO]: pepperoni21 joined the game
lobby-mc-1  | [16:26:38 INFO]: pepperoni21[/...] logged in with entity id 64 at ([world]-53.5, 75.0, 166.5)
lobby-mc-1  | [16:26:38 INFO]: pepperoni21 lost connection: Disconnected
lobby-mc-1  | [16:26:38 INFO]: pepperoni21 left the game

I set online-mode to false in server.properties and tried enabling bungeecord in spigot.yml but same issue.