My screen says v1.2.3, but 1.2.3.6 is the only close choice I have

I have a large (to me) XBox One world I have imported to Bedrock Edition on XBox One. Game save file is ~400MB

If I upload my world to a realm I can play for a couple of hours before it crashes (Elytra crashes it nearly immediately)

If I try to play locally My game will crash every few minutes.

I have tried:
Plutonium on/off - no difference detected
Render distance from min to max - no difference detected
various graphics options off - no difference

I have not found a particular trigger which causes the crash. Have not seen it crash as much on a newly generated world played locally.

The only thing I have found is to upload to my Realm and play - then again, it is fairly stable with the exception of not being able to use Elytra.
Still crashes when playing in my realm, just reduced to every 2 to 3 hours.

I have moved completely outside of the original XBox One 5x5 map area and the stability "seems" improved (again, when playing on Realm), lag is better at least.

Will try this world on iPad to see if game works locally there.

Hundreds of hours on this world and would like to be able to play it.

Like the expanded maps, but...

Am willing to invite a developer to my realm so they can download my map and debug the issues. I am certain they can re-create.

Playing on an xbox one S.