It looks like the player character is not setup correctly and is rotating around, which shouldn't happen. The player character should be functioning similar to the KinematicBody version of the platformer demo.
If you have not changed any of the settings on the RigidBody2D player, I would maybe open a issue on the Godot GitHub demo repository and see what they think. It could be that either something on the demo is not setup correctly, or something with the 2D physics has changed and the demo needs to be updated.
