SUMMARY:

When using a high definition resource pack, the game fails to automatically select a resolution that will allow the game to load.

DETAILS:

On January 14th, I attempted to log into my realm. Before connecting, it prompted me to download the texture pack. I assumed this means there was an update. I elected to download the update and it finished successfully.

I was then taken to the screen that's says Joining Realm... Loading Resources... Then Minecraft locked up and a black screen appeared. I was then taken back to the XBOX Home screen.

DEBUGGING STEPS:

• The first thing I did was clear cached data on the XBOX, by holding the power button until it shut down. That didn't work.

• Next I uninstalled and re-installed the game. That didn't work.

• Next, I moved the game from external to internal storage. That didn't work.

• Next, I downloaded my realm world locally. That didn't work.

• Next, I reconfigured the world and deactivated the VanillaBDCraft resource packs. THIS WORKED!

So, I proceeded to reach out to the developer of the resource pack...

     Discussion Here:  January 14th update crashes Minecraft on XBOX One X

They informed me that the game is supposed to automatically detect available memory and pick the highest quality based on my system's configuration, but that sometimes it doesn't get it right.  They explained how I could use the resource pack's settings "gear icon", to override that logic and force it to a lower resolution.

This solution worked.  

So...  That is one issue that probably needs to be looked into.  The reason I'm submitting it instead of using the workaround permanently is because other people joining my realm might experience the same crash and not know how to fix it. As well as other players experiencing the same problems with their own systems.

...And... The settings under Global Resources aren't getting saved, so every time I start the game, I have to go in and configure that texture pack with a limit of 128x.

     MCPE-62385 - Global Resource Settings aren't being saved

Here are two game-play videos, showing what happens...

Loading Fails with default configuration

Successful Load after configuring with 128x