`max-world-size` in server.properties controls the maximum size of the world border.
However if you are running a server for the first time, or set it after the world border is already set, the world border will continue to be larger then the `max-world-size`.
I'm not sure if this is intended behavior, but it's certainly confusing behavior.
I would have expected it to either have some other effect then being the maximum world border size, or for the world border to be at maximum `max-world-size` on launch.
If this was true previously, it definitely isn't now.
Tested on a new world, setting the max size resulted in a world border of the correct size, restarting with a smaller max size set, resulted in a border of the correct size. Sorry for wasting your time. @pokechu22