Inside of my guardian farm that produces a lot of lag, caused me to take a lot of damage, and then my game froze while the nether portal loading screen was still on my screen. I restart the game causing nothing to save and load back in. I try to see what the problem is and when I walk into a block that is 1 above the ground and another on top of it, I go straight through it. If I stay there for too long I will start to suffocate like I'm in sand. 

I could not reproduce the bug to get a screenshot. This bug is very inconsistent and random it seems.