Can create new worlds and they work fine for quite some time, but invariably at some point when I travel to the nether the game seems to lock up (seems to act like eternal lag).  Sometimes it is as I'm trying to portal to the nether and it remains stuck on the loading screen after portaling. Sometimes it is when trying to portal to the overworld and the portal sound runs, but the portal fails to actually activate.  Sometimes it simply stops reacting - I can move around, but it doesn't load new chunks, mobs all stop moving, and I can't place or mine blocks.  It will not allow me to access the pause menu to save/quit.  If I quit the app then when I try to re-open it, it gets stuck on the initial loading screen.  If I do a hard quit to completely quit the app from background running then when I try to re-load the world it will occasionally place me back in the last location I was in the overworld, but it immediately locks up the first time I try to travel to the nether.

I've found that if I edit the world files (by moving the files to my PC and using MCC Tool Chest PE application) to change the position to known safe coordinates in the overworld and set the DimensionID to 0 so that when I re-open the world I'm back in the overworld then the game seems to work fine for a while again (even allowing me to go to and from the Nether for a while), but will again lock up again at some point when I'm in the Nether.

A zip file with the latest example of the world files after a lock up is uploaded here: https://drive.google.com/file/d/1UYXQVprjSe2VqjhEgGNoGIslW4TGDdNw/view?usp=sharing