Solved, solution found here: https://forums.unrealengine.com/t/fps-drops-when-opening-context-menu-in-unreal-engine/731102/4
It had nothing to do with UE, it was Riva Tuner which is installed by default with MSI Afterburner (great HW monitor) but Riva caused all this mess 
After uninstalling Riva Tuner, no FPS drops on tooltips or buttons and most significantly, no FPS drops on Take Recorder!