By unpredictable place do u mean the hand just clip through wall? I had to mess with the physics parameter quite a lot like the amount of force, friction, bounciness ... but it still doesn't feel right sometime, and it's pretty hard to debug what went wrong in the physic when thing go flying or just stuck. I don't know how to do make it softer either, with soft body being quite a uncharted territory for me (I tested it a bit before in Godot and it is kinda broken). Also what problem did you have with the control? Maybe it was not unresponsive as it's stuck on wall? I made the hand and body force built up overtime until a max amount, so that could look like it is stuck.
Also I will definitely check out your game.