At randomized times, your head can go through blocks. This is incredibly annoying if you are going on bridges, swimming, or in the nether. I recently died on my smp realm because I swam into a block in an ocean monument and died because I couldn't mine myself out because of mining fatigue. I lost all of my mending Netherite gear, Elytra, and more. It happens at randomized times and has been occuring since before 1.16.100.