Trying to enter the world border from outside doesn't work consequently. Sometimes passing through works, and other times you get stuck inside of the border.
To reproduce:
set workdborder to 10
fly outside as spectator or teleport outside
try to walk inside
Quick video:
Everytging outside the world border is treated as solid blocks,, that is a deliberate design choice by the devs.
The only time you can walk back in is if you are at the very edge already.