As of the Udon additions to the beta, Teleport Player will randomly get deferred and break portals in my world.
You get warnings like this printed to the log:
2020.01.15 20:49:56 Warning - [VRC_TriggerInternal] ExecPortalTeleport deferred event TeleportPlayer type Custom because waiting for TeleportTarget to ready
Repro: go to my Camera Test world wrld_91805f98-fd56-497a-bf7e-772e434efb84
Turn on portals, and turn to the right and go through one of the portals while facing it. You will probably be left at the portal and see the stars instead of having gone through it.
The deferred teleports don't seem to happen as much if you go through the portals sideways.