Hot tub breaker
Like the other posters are saying, it's most likely not a bad breaker. Twice I have had the heating element go bad on my HT which I replaced myself without any issues. It could be many other problems, but trying this is easy and you can test it without draining the tub. Get a multimeter and ensure the power is off. Remove the wires/connectors from the heating element screw terminals. Test the resistance (ohms) between one of the terminals for the element and the metal housing. Repeat with the other terminal. If you get any reading, it shows that current is flowing from the heating element, through the water to the metal housing. This condition would trip the GFCI breaker and indicates you need a new element.