The warm moist air from the bathroom is cooling and condensing in the pipe from the exhaust fan. It sounds like the pipe goes up and the condensation is collecting on the inside walls of the pipe and running back down into the bathroom. You may try rerouting the piping so that it only rises enough to clear the insulation and then direct it out the side of the attic space with a gentle downward slope so the water runs outside.

Check to make sure the vent is insulated and also if you replace the vent tubing try to use something with a smooth inside like galvanized, or PVC venting. The flexible venting tends to have more back pressure and does not move the humid air out as well as a more rigid and smoother vent tube.

The above answers are good. Also, please check the owners manual for your fan, or contact manufacturer’s customer service.

The drip that you mentioned is caused by condensation collecting in the duct work that runs from the fan to the roof opening. You need to check the piping and possibly use insulated flex pipe or check the flapper in the fan to make sure it closes when the fan is off. For some reason cold air is getting into the pipe and causing the condensation drip. The pipe may have come loose from the roof opening?

try insulating the pipe that vents to the roof to stop condinsation
also try to see if thair is a flap that opens when you turn the fan on and should close after its shut off blocking any warm air from getting to the pipes wile not in use.