Frequently, turning on the tub without the proper amount of water in it can caused damage...and you did it multiple times? Long enough to video it?
However, your supposed hot tub is working fine.
Seriously, if your getting voltage to the heater, and all the plugs, as you say, it's working perfectly fine.
It might help to actually know what hot tub you think you have. Like a brand, model, year etc. (believe it or not, over the last 35 years or so, there's been a LOT of different hot tubs with different designs, configurations and electrical set-ups...hard to believe, I know). Also exactly how you're testing for the voltage you say is there.
*waving cane* GET OFF THE LAWN YA DAM KIDS