Too many crashes

I would like u to fix the crashes. Like for example,
I go on worlds and it starts to lag and glitch (thats another problem Im having)
And when I build an awesome structure it crashes and when I go back on it doesnt save and its really annoying. About the glitches and lags, it makes a huge glitch and then it crashes.
Every time it crashes!!!! Pls fix this! Other than all this, the game is awesome!

about Blocksworld HD, v1.29.3