Flying in survival

After loading the survival world, my brother asked me why I was sliding around and pointed out that I had air bubbles over the hot bar. After that, he decided to join the game. He spawned in at world spawn even though he had played on my world many times, he went to jump and realized he was flying. We left the game and reloaded after taking the pictures below, the same thing happened. After that we left, hard crashed the game and reloaded. After spawning in we played and all was normal until the game crashed 15 minutes in and we had to reload again. Everything seems fine after the 5th reload.