Erik Kostson
Ansys Employee
I think the main issue here is that the face normal of the top and bottom faces should be pointing in the Z-direction just as it does below in the example I did (in the image you show they are pointing in the Y direction - so the plate (width x length) should be in the XY plane and the plate normal is Z). This is described a bit in the help manual under solid185 (element reference).
Try that (so width along Y length/long direction along X and thickness direction along Z).

Also as we said can you try to add the BC not on the edge but on the nodes half thickness up from the bottom face so on the midplane so to speak a I did here on the bottom 3D part (try the first above and if this does not resolve try this, but it could make little difference as the plate is very thin):

As for the delamination I think you need to model every lamina/ply explicitly (so every layer is a volume and part) I believe and then disconnect nodes to represent like a crack between plies/laminas in a modal analysis and to see how this changes the modes - perhaps there is some material out there that can help.

All the best