Outdoor GFCI circuit. This powers a transformer connected to a string of walkway lights mounted in a masonry knee wall that forms the front wall of a 40' long planter box, having a masonry fence wall as its other side. Planter was washed with hot road patch tar to waterproof the planter, which has a french drain about 3.5-3 feet down from the soil surface, over which is 8"-10" of gravel, over which is about a foot of soil, and is fully planted and has an automatic irrigation system. Transformer and GFCI are surface wall-mounted away from the planter area and not exposed to irrigation, but are in direct sunlight. We're in hot desert climate - Scottsdale, Arizona.
Transformer filed 2X in 3 years. GFCI periodically trips, but has allowed reset until this last time. GFCI will not reset (no "click").