What is the fps of the Switch version?

720p 30 FPS, docked and portable.

Unreal Engine 4 is bloated and was not made with a somewhat weak platform in mind. To my knowledge there is no  UE4 game running on 1080p 60 FPS on Switch, not even first party titles like that new Yoshi game, which runs at 720p 60 FPS docked. If DICO was a better developer they probably could manage to get the same result with Bloodstained, but as you can see with all these bugs and even framerate drops on a much powerful console (PS4 Pro), they aren't exactly competent.

When you mean terrible slowdown, do you mean vanilla Odin Sphere Odette boss fight bad(lags so badly the boss's attacks are way more telegraphed due to slowdown) or Code Vein slowdown( one fire effect in the camera, everything chugs)?