Pretty sure that's because the player's head goes above the gap so you can't move forward (the player jumps 1.25 blocks without any outside interference)
The way I deal with it is pressing cancel and then trying to go in again, that usually works after about 10 seconds of loading for me.
Pretty sure that's because the player's head goes above the gap so you can't move forward (the player jumps 1.25 blocks without any outside interference)