Hi,
Could I ask you to try reproducing this in a common Epic sample project such as RealisticRendering?
You should enable the in-editor frame-rate counter when you do so, that way you can tell me what the editor frame rate is (in FPS & ms/frame):
From the Main Menu, select Unreal Editor > Preferences… > General > Miscellaneous > Performance > Show Frame Rate And Memory
Please also attach a summary of your machine specifications, or better still a system profile which you can generate using /Applications/Utilities/System Information.app, so that I know what kind of CPU, RAM & GPU setup you have.
I’m not able to reproduce this on a 2013 , quite understandably if it is a frame-rate related problem, but nor am I able to reproduce the problem in RealistcRendering on a 2012 MacBook Pro with Nvidia 650M. Are you running with a realtime viewport enabled? (Viewport options are in the top-left corner of the viewport - the unlabelled down arrow).