Flickering with placed actors in oculus source 4.27

after installing oculus source 4.27 , this is the i have been facing all the placed actors flicker continuously

i cloned source engine then setup and generate file and build after that i setup android
and when i create a new file this happen flickering with player start lights lightmass portal postprocess and so on …
it worked fine in normal version of ue4.25 and ue 4.27