This first happened when I decided to explore riding on horseback. While moving around, chunks in front of me will load, but I am met with an invisible barrier. Mobs nearby were acting weird (jittering when crossing the invisible barrier) and wouldn't move, on one occasion I fell into the water (did not float, as if there was no water at all) and was being attacked by an invisible mob until eventually killed me. This has happened multiple times already and in different parts of my world. Also, sometimes when entering the world I would instantly die for no reason.