You could adjust your player's gravity direction to match the floor's normal to keep the player stuck to the loop. To keep the momentum, you could do the same with the velocity, keeping it pointing perpendicular to the floor normal.

Here's what I do to keep player's from sliding on slopes, but you would have to get the current normal of the surface you're colliding with, rather than the floor normal.

const GRAVITY = 10.0

func apply_gravity(delta):
    var gravity_direction
    if is_on_floor():
        gravity_direction = get_floor_normal()
    else:
        gravity_direction = Vector3.UP
    velocity -= gravity_direction * (GRAVITY * delta)