Update on editor fps drop issues while right click is held and released on viewport:
We narrowed down issue the issue to HitProxy calculation logic while editor camera is flying. There is a code piece where editor stops updating hit proxies while you’re flying with camera (because technically you can’t click on actors while flying with camera). The problem is, when you stop flying (aka, stop holding right click), the camera still moves a little bit with deceleration. During this deceleration, HitProxies gets invalidated each frame until camera is fully stopped, which causes huge cpu spike.
We solved this with a workaround in Editor/UnrealEd/Private/CameraController.cpp:
https://github.com/ShadowfallStudios/UnrealEngine/commit/85798d0f9d7378f7d3d41f9f31cf22340c42abfd
If you cannot access the link, here is the actual patch:
This patch makes camera stop immediately after you stop providing an input. Not a good solution, but still better than fps drop.