You have a short to ground somewhere in your hot tub light circuit.

You need to find an electrician who works on pools to help you find and correct this potentially hazardous condition.

GFCI especially GFCI Outlets (this is how your circuit is protected) can fail closed, meaning the Ground Fault Circuit Interruption circuit stops working but power still passes through the outlet and to the downstream load. If this happens, the short in your hot tub circuit could find a path through a swimmer.