Capacitive coupling can generate nasty 'stray voltage' in UL listed hot tubs. It is essential that there be a true ground path from the exterior GFCI receptacle feeding such a tub.
Body salt accumulates in the hot tub making it increasingly conducting....
As installed, the hot water is pumped vigorously through motor field windings -- stray magnetic leakage is enough -- the pipes are plastic.
The end result is a "tank circuit" with a potential of over fifty volts from hot water to the wet surround. ( An actual situation; solved by running a 'bleeder' grounding conductor to the GEC by way of the all-copper cold water system.
