Steps to reproduce:
1) Play minecraft with at least two players locally in split screen. In this example thare are two players.
2) Press the power button on the Switch console to go in sleep mode and disconnect all controllers.
3) Press again the power button and return to the game
4) Press L+R and than A on the first controller to synchronize player 1.
5) Press L+R an than A on the second controller to try synchronize player 2.
6) The game will do again a synchronization but only for player 1 (Returning to Step 4). So player 2 can't play unless reloading the world.
The game should do a new synchronization for all current players instead of only the first one and must not show the synchronization two times.
See the video for more details