After downloading the second preview of 4.13, which fixed my earlier issue with 4.13, I’ve found that over time the engine just ‘decides’ to begin rendering the scene multiple times which obviously drastically reduces performance, I’ve included a screenshot of PROFILEGPU
As you can see there are multiple scene renders per frame.
(This issue of course did not exist in 4.12, but not sure if it was in Preview 1 because I never used it for very long due to my other issue with it)
[EDIT] Restarting the editor resets the scene render count and I can’t find any specific way to catalyse new scene renders - it seems to just happen over time.