Repro in this world: a player can drop a portal that appears to be valid, but if a remote player has a spawn transform at that location, the portal will disappear. The three cubes in this world are spawn transforms, but the pickups are not synced. If one player places a cube on the green circle, and other players remove all cubes, the other players can drop a portal at this location but it will immediately disappear.

Discussion:

Udon allows spawn transforms to be moved. It makes some sense that remote players should not be allowed to drop portals onto your local spawn, however, it is confusing in-game as to why what seems to have been a valid portal suddently disappears.

This behavior also invalidates methods of preventing portals to be dropped by some users but not others by locally moving spawn transforms, as may be desired by event hosts.

Previous versions of this method were valid as a spawn transform set to a player location acted the same remotely, as being too close to a player. Now, in order to prevent a given player from dropping a portal, a large area needs to be covered, and effectively means you cannot control which players can drop portals any longer. This means that functionality available on live will not be available once the open beta is in place.

Now that portals have an option to confirm, perhaps revisting placement might be useful as well.

Possible suggestions:

Related to this: https://feedback.vrchat.com/feature-requests/p/expose-allow-portals-to-udon