Electric breaker tripping without anything plugged in
I would bet that the breaker is toast. GFCI receptacles for outdoor use are required to be WR or weather resistant rated. I have not seen this listing on the GFCI breakers I have installed. So if it got wet from the door being open and trips it sounds like time for a new one.
You could always swap a working one with the one that keeps tripping to see if it’s possibly a real circuit issue.
If that breaker continues to trip it’s time to replace it. Molded breakers when faulty are by code not repairable. Could it be dried out like a cell phone? Maybe I have never tried this.