Both are possible and the order of suspicion matters. A GFCI that trips with nothing plugged in and will not hold a test is often a tired device, and replacement settles it. A GFCI that trips when a specific appliance runs, or after rain at outdoor and dock locations, is reporting ground leakage from that appliance or water in a box, which is the device doing its exact job. At docks and pools, treat every trip as real until an assessment says otherwise, and keep people out of the water near a faulting circuit.
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