Hi,
It nvarguscamerasrc ! fakesink can pass 5566 times in loop, the source looks fine and the issue probably is somewhere else. Please try to apply the whole pipeline to the sample and check if the issue happens. You can make sure the pipeline is good in gst-launch-1.0 command first and then apply the same to Gst.parse_launch()
Here is a gst-launch-1.0 command for reference:
Could not link nvarguscamerasrc0 to nvstreammux0 - #10 by DaneLLL