Tree Colliders Enabled causes First Person Character to fall through Terrain?

I have a rather large terrain with several trees and details. Everyt$$anonymous$$ng worked fine w$$anonymous$$le pressing play over the last few days but now I am encountering two problems w$$anonymous$$ch seem to be connected:

When Enable Tree Colliders is checked, my First Person Controller falls through the terrain.

When Enable Tree Colliders is unchecked, my First Person Controller is just fine and stays on the surface.

On a related note, I am unable to place anymore trees or details. I have not added anyt$$anonymous$$ng nor have I altered anyt$$anonymous$$ng. These two issues occurred at the same time and was easy to diagnose thanks to previous Answers here.

I've tried everyt$$anonymous$$ng I can t$$anonymous$$nk of.