port inhomogeniously filled error

I am not sure, but have you tried increasing mesh cells or mesh line limit ratio!

The first change after Cross section of the port you are defining, is the problem
the port must maintain its shape at least for a few mesh cells.
Then you may increase the distance between the port and that first change.
I wish it will work...

You can also change the reference plane and use a longer feed line. Or increase locally the mesh cell density.