Game connection lost when using a portal

Beta 1.18.20.25 on xbo One

 

Twice when using a portal to travel from the overworld to the nether I have lost game connection

 

Both times this was from the same portal, but on other occasions this portal has worked normally.

The nether loading screen flashes briefly before changing to a generic brown colour, and connection is lost within seconds. 

 

I just get dumped back out to the xbox menu.

 

On reloading, everything seems okay, nothing missing and the portal works fine.