Character and world become de-synchronized

My world has increasingly become laggy and/or my character is no longer in sync with the world.  Right now I am working on a guardian farm area, so I have the space of water monument enclosed with a large square wall.  I have probably more than 50 axolotls in there keeping the guardians off my back.  Periodically, I swim around to pick up the fish and other drops floating at the top of the water and suddenly I'll still be swimming, but I'm no longer picking things up (inventory not full) and the axolotls and guardians around have stopped moving.  i can't open chests.  The only way I can seem to fix it is to force-close the app and re-start.  If I break blocks, they will disappear from the space but the item doesn't appear.  

Periodically I will also get lag where the game takes a while to respond to either opening a box or sleeping on a bed, but that eventually catches up.

I'm not really sure how many mobs is too many, and I suspect it has something to do with all the axoltols I have swimming around - but honestly, if the game can't handle that many, maybe there should be a better way to express that than to have my world lag out/de-synchronize all the time. And I really don't want to have to kill all the axolotls I am ending up with in pursuit of a blue axolotl.. 

This is a single player world, not on a realm or server.