IF Its Ray Traced. You are moving geometry and asking it to render a shadow in real time.
of course its intensive performance wise. You would need to fine tune the level at which the shadow is traced, vs cascade, vs DFAO
first try to Disable the shadow completely and use DFAO.
Tough not with the models you are showing. A single blade of grass would need a DF resolution bump of 4 or more to render the static shadow somewhat decently.
either way, check performance. If you get an increase then all good. If not, bottom footnote.
Assuming you see a change, You can also try the nvidia rtx release of the engine. Its a little more performant, but you miss out on any hot fix to the engine until someone at nvidia updates the branch.
plus you have to compile it. Which takes time.
Additionally, the shadows you see could just be cascade (since Ray trace option is off).
Disable cascade distance or resolution to check before you blame Ray trace for the cost. Ot could just be normal feeding on the cascade settings.
If the mesh is doubled by a setting (i would wager it isnt). Do a stat RHI and get both tris count.
If you are correct, a count is more than another.
If my hunch is right, then maybe you painted more than one foliage in the exact same spot/size/rotation and one of them goes off time because of the fps drop, allowing you to see it.
Generally speaking if you use Ray trace you go for fully dynamic, so you should not be baking. A hybrid can be made to work well, but it needs major fine tuning.
Refer to this as a guide. Lots of stuff to toggle and setup.
Depending on hardware, just enabling raytrace in project settings can drop performance to a halting 5fps grind in the default levels. If that’s the case for you, you just need better hardware.