Do I need to ask if you transported it with the tank either empty or removed?
It's possible that it's died a early death. Electronics fails either early in life or out at end of life.
The failure versus time curve is described at a bathtub curve.
For military use, electronics are "burned in" for some hours and temperature to weed out early failure.
They should do this with medical equipment -- but likely do not. It goes to the end user; and if it dies, they replace it.