If i ever try and join a old world that was created before this update it crashes everytime and also for realms if your world on the realm was created before this update it will say Unable to connect to world. Also if you upload a new world to the realm thats created in the latest update it says disconnected
To see if it crashes for you do these steps
Open Minecraft on Windows 10'
press play
try joinning a world u have created before this update
then it crashes
so sorry i have fixed it now it was just a addon causing a crash so sorry for wasting ur time looking at this
Closing as Cannot Reproduce as per reporter's description update.