UE4 freezes occasionally

UE4 freezes(unresponsive) for 60sec on scene but does not freeze on first creation of a project, and only freezes on the second,third etc launched. UE4 freeze at an interval 2-4mins. The output logs does not give any errors or warning.

I have just changed my gt 620 to gtx960 and wasn’t experiencing this issue at all before. Please help…

CPU: Intel e5-1620
GPU: gtx960 MSI
Motherboard: Intel DX79TO

The issue was with UE4 4.12.2 version, i moved to to 4.11.2 and no freeze occurs.