Massive lag is certain situations. Game runs fine in most cases. When I run into a mob spawner in a cave the game will start to lag to the point of being unplayable. This does not always happen immediately. Sometimes I can kill dozens of spawned mobs right near the spawn trap and have no issues for a while. Other times I just need to be close to an area with more than a few mobs in it and it will lag. When it lags, button presses are severely delayed. I press a button and it registers a second or two later and treats the action as a long button press rather than a tap. Turning or moving the camera angle is nearly impossible at this point. This behavior continues when I try to adjust the settings with the world still loaded. Even the menu is affected. Graphic rendering slows to a crawl and then stops all together. Exiting the game, rebooting the device and reloading the world I can only see black or shades of blue and the character is still stuck in "quicksand." The health, armor, inventory, ect. overlays still show, but no blocks. Occasionally I can see very slow torch animation "sprites" but that is all.

Now, If I can move far enough away from the "source" of the slow-down, everything returns to normal. Full frame-rates and responsiveness. I can take on scores of mobs outside with virtually no lag. I can create underground rooms with mob spawners of every type of mob and fight them indefinitely with little or no lag. If I can close off the open wall of a spawn trap before the lags hits, I can return over and over again to the same spawn trap and "farm" the mobs without issue.

However, once the lag starts, If I return to the same general area of the source of "slow-down" the game grinds to a halt and is unplayable again. The distance from the source and the degree of lag seems to vary from case to case as well. Sometimes its only a small radius of blocks and sometimes I'm "lag-holed" out of most of a very large mine. I've no clue why the lag is only occurring in certain situations and places where mobs are concentrated. The game-stopping lag has happened on freshly started worlds, well-established worlds, survival mode, creative mode, different types of mobs, different biome(s), day, night, varying inventory and armor...

Fixes I've tried already:
1. Setting all graphics to lowest setting, turning off sound and wifi.
2. Uninstall and reinstall the game, clearing cache.
3. Testing new worlds in both creative and survivor mode to see if it was individual file corruption.
4. Making sure I have more than enough free ram before starting the game and while running it.
5. Developer options: limiting background processes to no more that two, force GPU rendering, turn off hardware overlays and turn on 4xMSAA. (both individual and combinations of those options.)
6. Swearing. Lots of swearing.