Near one of the control points, a gap appeared in the terrain close to where a Supply Pod had landed.
You are able to jump into it and run around a little before "Out of Bounds" warning appears. Though there were a few spots where the player is able to stand without the timer.
Unfortunately I have no steps to reproduce as this is a Mixtape map and not always open for me to quickly check.
For reference, I was playing as Alter and had used Void Passage through a wall nearby when I stumbled across this.
If I can reproduce in the future, I will update this ticket accordingly.