I added a GameObject that has VRCPlayerObject, VRCEnablePersistence and companion UdonSharp component in a existing world and done "Build & Test".
It worked in the VRChat live app, and in the first attempt, worked in the VRChat persistence beta app as well, including rejoin.
But in the second and third try with VRChat persistence-beta app, rejoining caused infinite world loading loop.
The log says
[Behaviour] Resetting game flow because "Failed to join room for unknown reasons": [TryAlternateInstance, SkipLogin]
and finally I have blocked by "Failed to authenticate with realtime servers: Too many requests"!