I can confirm lag happens for me too, simple landscape, small water plane, I went from 8 ms (120) to about 11-12ms (90s ish)
I dont know who is going to look into however, someone has to step up to the plate and I can only do a little to keep things rolling here.
So** please heed the Calling, O Brave and Adventurous UE4 programmer **who has more time than me,
Thine time to shine has come!
