Video speed randomly changes but audio speed stays the same

[pepijn]

Action
Action Version: 1.31.3.0
Recording Resolution: Original
Screen/s: 120
mic and audio: seperated
Recording Mode: Game

Windows and Hardware
OS: Windows 10
Video Card: NVIDIA gtx 760
CPU brand and model: Intel Core i7 6700k
Memory: 16 GB
Monitor Resolution: 1920x1080

Problem Description
Game/App Problem: Speed of the gameplay randomly changes first normal then fast and then normal.
But the audio stays normal so you will see that its not synchrone any more(please see picture from vegas)
I could not upload the footage here so uploaded it on a random stream site http://sendvid.com/zak2um7i

[pepijn]

any update?

[pepijn]

just got a gtx 1070 but still the same problem but now its most of the time just one frame per second or less but my game runs still at 50fps(4k resolution)