Still. It happens. The lagging. The crashing. I'm 64 yrs. old and want to live long enough to play this game without serious issues. Officially putting you on my prayer list now.
I have this issue also. Thought it was from natural pack but even after removing and buying a new texture pack I still get crashes and the 'you are out of data space' error message. I deleted all extra worlds except 2 and my realm. Just now got another crash on a new world. Please get this fixed!
The way I've worked around the treasure chest issue is to make a new world with the same seed. The treasures and everything else are in the same places. Just a matter of using xy coordinates of where the chests are buried in the new world, and going to that location in the old world. My old world is too developed to start over again.