Performance loss when switching between cameras

Hi Guys,
i am facing a very strange problem (using UE 4.21, happens also in 4.22 preview).

I have a *CineCamera *in my Pawn, the game is running with over 100fps. Everything fine.
At some point I need to switch the camera. Therefore I’ve created a LevelSequence with another CineCamera in the Cameracut track (exactly same settings like the camera in the pawn) and I play this Sequence via Blueprint. The peformance drops down to 15fps!
Then I have also tried to switch to another camera via Blueprint directly (via ‘SetViewTargetWithBlend’) - the same effect here. FPS drops down to around 15fps!

Why is this happening? Does the engine still rendering the pawn camera in the background?
I really would appreciate your help! Thanks in advance!