ATM10
MC Version 1.21.1
Mod shows up to date: 5.1.1
Multiplayer server.
Not near spawn.
Not finding a lot of people reporting this, however I do see a few people on the ATM10 discord asking about it.

Seems the expulsion pylon doesn't work despite testing different places and settings.

I believe I figured this out.

It seems FTB teams are considered when pylons is trying to expel players.
This interaction between pylons and FTB teams was not documented from what I could find so I was having a hard time figuring it out.