Summary

Whan you move at specific coordinates (absolute value=2^n ,such as 65536) and move towards that axis at specific speed{[20*2^(n-24)]m/s towards that axis}, your hitbox width will change.

Steps to Reproduce and Observed Results:

1.Create a superflat world.

2.Run /tp @s 65535.5 -60 0 facing 65536.5 -60 80

3.Walk for about 8 seconds.

4.You will find that your hitbox become narrow and could walk into 0.5 blocks wide gap.

5.Run /tp @s 65536.0 -60 0 facing 65535.0 -60 80

6.Walk for about 10 seconds.

7.You will find that your hitbox become wide and couldn't walk into 1 block wide gap.

Expected Results:

Your hitbox do not change.