If you add both surfaces as reference surfaces and then look at the properties of the surface slices in the template editor - try applying the curve adjustment property
Also try changing both surfaces to type design so that they get treated the same way when being sliced .
The challenge is that the surfaces are generated by chording curved linework so if they have sectonal lines at the same stations they should match at those locations if they really do match - but in between sections in the model they likely don’t match - that is what the curve adjustment is for.
Send me the project you are looking at and I can take a look
For the vertical lines - they can be clipped to finish grade when you add the surface instruction to the corridor if the FG is wide enough - if not you can add an offset elev to the left and right end of FG to make it wider and then clip the subgrade to FG and that should fix the issue
This post covers the issue and resolution in some detail Frank
Alan