Or is it the main fireplace chimney that has a crack or blockage, and the fireplace has a gas line?

He spent about 15 minutes with it and the wipes were never ending so he informed the tenant that per their lease any tenant caused blockage is their responsibility so they would need to call a plumber (we always do the first one for free because it could have been from a preexisting issue).

Likely a blockage in the sewer line.

1) Small Animals, skunks have been persistent this year.2) Plumbing blockage due to tenant, I clearly indicate that's not in my scope of work.

This crimping of the line causes blockage issues with leaves etc. so you may want to look at the angles and connections.Also if the gutters are not attached properly the water can run behind instead of draining down.

For example, my lease says (in part): "Tenant shall be charged for repair of drain blockages or stoppages, unless caused by defective plumbing parts or tree roots invading sewer lines."

There was a blockage in the hose and it caused substantial damage.

@John Underwood I'm probably going to specify them for general blockages in future leases, but I'm not sure what's standard.

Check the outlets on the French drain and look for blockage (leaves and debris) along the drain as well.

The inspection found out there was sewage problems with blockage.