Guilin Sun
Ansys Employee

I believe it is not resolution issue, as I can see the mesh is quite fine. The issue is to understand them:
you are visualizing the magnitude of the field, not the real or imaginary part of the E field. Since in the transmission and reflection, the amplitude is fixed.

The fringes shown are due to interference.

If you visualize real part of Ex, Ey or Ez depending on your source, you will see different result: