I just tried to find what is wrong with your project, do not use mine, instead look what i changed. I didn’t care about playability i wanted to find your problem and solve it.
I turned off gravity for the box, it was sometimes falling to ground and doing that random spin after collision. I think i know what you want and when i have some time (after work) i can do hoovering vehicle quite fast. Sadly hoovering component behaves weird, so easier way is to make hoovering blueprint and attach 4 of them to box. I have quite good idea for it, it also can be used to make antigravity ships. So will probably use this idea some day for racing game.