Improve the controllers by moving the battery spring to the bottom end.
Playing Beat Saber on Expert +, the controller will disappear during large swings. This is caused because the spring holding the battery in place is at the top of the controller battery compartment. Large, fast swings will cause the battery to compress the spring and lose contact at the bottom. The power briefly goes out and the controller drops from the game. If the spring was on the bottom end this would not happen. Other suggestions would be to add in a capacitor to hold charge if the battery was disconnected or as others suggested switch to a large rechargeable battery.