Hot tub gfci's should be tested frequently to ensure functionality
To do this press the test button, this should shut the breaker off instantly, If it does not shut off, the breaker may need replacement.
Gfci's have a lifespan and get weak over time or can have factory deficiencies causing them to prematurely wear, in a cold climate like ours its a good idea to have them checked every now and again to prevent freeze damage if it shuts down without your knowledge.