I have a problem similar to this: Downstairs half bathroom, ceiling exhaust fan dripping, first noticed during very hot weather. However, the amount of water makes me think it is not condensation. Also, the downstairs doesn't have AC, just the upstairs, so the temperature difference would be smaller.
The dripping is not constant, but so far I haven't found a pattern. I'm not sure where the fan vents to, probably the soffit.
From attic crawl space I cannot see along the joists between which the fan sits (hidden by chimney, which itself is dry), but the neighboring joists & ceiling appear dry. The fan housing itself can't be removed without being destroyed, so investigation around the fan will involve removal of drywall. There is an upstairs bathroom nearby, but neither the sink nor the toilet appear leaky.
Single family home ('78), the second floor was built on in the nineties. AC unit sits in attic, pipes run in exterior wall far away from issue.
What would be the best line to investigate, and should we get a plumber, handyman, ...?