Framerate "stuck" - Graphic settings wont change anything


again I have massive performance Problems within the Unreal Engine 4. I have one map that is stuck with low FPS and a very high render time. I currently have 6 large scale maps finished and 5 of them run extremly well with 60-90fps. Another map with the same assets and settings (just other light angle & color) is stuck at ~50FPS and 20ms render time which feels extremly like extrem lag and it’s just no fun to play.

I’m using two sided foliage with distance culling and a dynamic directional light. Changing the graphical settings won’t change anything relatet on FPS. Even looking on the ground won’t increase the FPS like in all other maps.

The Frame lock is set to 120 in this example and I have absolutly no idea what’s going wrong here. Even no grass and shadows rendered and the GPU load is extremly high.I already tried Ray Traced Distance Field Soft Shadows but that hat absolutly 0 impact on the performance.

Recreating the map is almost not possible for me, my time scope is extremly tight right now and it’s getting extremly frustrating. I btw have still [the massive performance problems][1] that I can only use the directional light to cast shadows, all other light sources woud ground the FPs down to <15 but that “would be ok” if I can’t fix this now.

Im running with this system:
CPU: Intel Xeon E3-1231 v3
GPU: Sapphire R9 290x 4GB
OS: Windows 10 64bit

I reinstalled the system ~a month ago. I would be very pleased if someone out there would have any tipps for my. There must be something terribly wrong …
Thank you very much.