That is a common problem in HFSS.
The 3D modeller uses true curves. But the solver uses linear meshes even when the EM field is solved in curvelinear coordinates (there was no such option 10 years ago, but the modeller and the mesher did not change much since then). Usually, every iteration will produce a new mesh which will eventually intersect somewhere. There is no mechanism for avoidint this problem in HFSS.
Your only option is creating a linear (triangular faceted) mesh outside of HFSS and importing it as is. Faceted objects are re-meshed without distortions when solving.
Another option is creating a buffer dielectric layer where all your metal patches reside completely, so the solver will substract the iterative mesh automatically from this layer wtih no errors. This can be simply an airbox and the metal patches "floating" above the substrate in it.