CST MWS simulation of a rectangular waveguide

I am starting off with a simple case of lossless dielectric filled waveguide with lossy dielectric segments on it's sides. I did a parameter sweep varying loss and looking at Ez. I am interested in TM11 mode and hence would like Ez to be high. I am using the transient solver to run this.
I put in curves at the input and output waveguide ports which are located at the ends of this structure. Also there is a curve along the center of the waveguide. I am evaluating Ez along these curves for a fixed time.

The behavior of Ez along these curves is not as expected. I am seeing some growth instead of decay for some loss tangent values. I am also seeing ripples at the input (z=0)(see attached). The output (at z =10) curves are smooth compared to the input.
For this simulation, am exciting port 1 just with one mode i.e TM11. But am interested in looking at how how much I am losing to other modes. But am not sure how to do that yet.
My question is, am I doing something wrong in the way I am evaluating the field strength. How do I look into how much is going into TM11 ( in my case mode 8 out of the first 10 modes)