BEFORE you waste any money replacing that breaker,.......
I'm with kb. The failed GFCI breakers that I have seen just failed to reset, even when the load was completely removed. I am not aware of any GFCI Breakers that somehow became more sensitive, and tripped at less leakage than the original set point.
In the real world GFCI feed circuits that have some leakage current. That leakage may be very small and just due to line leakage or more so, the a total from the UL permitted leakage of
0.5MA per device. That is only 1/10 of the permissible but it is
cumulative to the total number of UL devices on the circuit. The GFCI is dumb, all it knows is that when the total leakage >5mA it will trip. The GFCI cannot differentiate between which of the loads that it sees are <5mA and which is the load that will make it trip.
When there is nuisance tripping on a GFCI remember it's the total current. GFCI breakers are often connected to many misc. loads that are not associated with loads that require GFCI protection Examples of this include lighting and receptacles not in GFCI areas or even just very long circuit runs (e.g.>100')
I would trip the GFCI breaker in question and make a list of all affected loads, lights, and receptacles. Any of these that do not require GFCI protection should be on a non-GFCI breaker. If list has more than one load or if there is a long run between the GFCI Breaker & the load, I would substitute a std Breaker for the GFCI and Install a GFCI near the Hot Tub to feed the Hot Tub components that require GFCI protection.