Mining west at from x = 4608 all changes I make to blocks at x = 4607 and lower are lost once I move > 125 blocks east or if I leave the game and re-enter. This is true from y = 7 up through the surface (e.g., y = 72).  The two houses I have east of x = 4608 remain unchanged, but it appears that all structures west of this delineation no longer exist. I believe this occurred October 11 or 12, 2018.

If you mine the affected blocks, all seems normal, but if you leave the game, then re-enter, you materialize inside the blocks and quickly die.

I do not know if this affects the entire remainder of the world since now I cannot easily travel between the sites I've created (4-5000 blocks in each direction from 0,0).

This appears similar to MCPE-15722, but not identical and a different platform.