Note: Bug found while playing All the Mods 9
The Bug
I dialed Cavum Tenebrae from the overworld. I stepped through the gate. Did not move while I took in the environment. As soon as I moved, I started being continuously pushed to the left of the gate. Jumping accelerated the rate I was moving in that direction.

To Reproduce
Reproducible by traveling to Cavum Tenebrae and moving the character. Will happen even after restarting game. I later joined a friend’s world to see if it would happen again and it did for both of us.

Uh, Cavum Tenebrae has a black hole for a sun, pretty sure the pull is a feature.

This is not a bug. It is indeed a feature.

Cavum Tenebrae is a planet near a black hole that you can see in the sky.

The gravity changes depending on the time of day.
You're always being pulled towards the black hole.
This means that at noon, when the black hole is directly above you, the gravity is weaker and you can jump higher, while at midnight the black hole is behind the planet, below you, and the gravity is higher.

And in between, the black hole will be on either side of you and therefore gravity will push you sideways.

This is also why Cavum tenebrae looks the way it does.
The black hole's gravity is tearing this planet apart.