as “question” is already stating:
my UE4 itself wont update its frame only if i tab out and in again.
i had the same problem with fortnite too and i seriously dont know how i fixed it since i only switched forth and back to borderless, fullscreen and windowed.
anyone out there who has the same problem or a fix already ?
System:
AMD FX 4100quad 3.6ghz
AMD R9 280X Matrix
(listing those because i know amd has problems with UE4)