This bug requires to enable the new b-frames fix see: https://devtalk.nvidia.com/default/topic/1056338/jetson-nano/gstreamer-h264-encoder-bug-gstv4l2h264enc-h-num-b-frames-is-set-to-boolean-instead-int/post/5359591/#5359591
It appears that the nvv4l2h264enc encoder is setting the display timestamps the same as the decoder timestamps.
A strict player will show the lack of proper order of each frame i.e. IPbbPbbPbb… instead of IbbPbbPbb… (Other players will skip one of the b frames and it might looks like if the video is a lower fps )
This issue is not happening on the NMAP 02_video_encoder sample SW.