GFCI circuits are not usually connected to lighting circuits. This is why you usually find that bathroom and kitchen outlets, but not lights, are on the same circuit. This is not universal. I would suspect either there really is a breaker tripped, the breaker is defective, or perhaps there is a loose connection somewhere in the lighting circuit. I literally just had this happen. My living room ceiling fan just stopped working after years and years. The circuit it's on is fine. I traced it to a junction box in the attic, that runs to the fan, where the power wires had come undone from the wire nut. Go figure.