I had a survival world and when I left then rejoined I randomly sank through the ground and blocks rendered in the spectator mode.
You keep sinking until you reach -0.05400 y and chunks start glitching out like only in certain spots they render. The game also locks up or lags out bug like if it has no connection because you can still move just not break blocks or chat and other stuff like that.
It fixes itself once you rejoin.