Gstreamer loses frames while encoding usb camera with rtsp camera

You can check if the v4l2 source runs well:

gst-launch-1.0 -ev v4l2src device=/dev/presentation ! queue ! tee name=t1 ! video/x-raw, width=1920, height=1080, framerate=30/1 ! videorate ! video/x-raw, width=1920, height=1080, framerate=30/1 ! nvvidconv ! fpsdisplaysink text-overlay=0 video-sink=nvoverlaysink sync=0

If no issue is seen with the pipeline. Probably CPU cores are at full loading and impacts the performance. You can run sudo tegrastats to get system loading.

Hardware converter is also heavy in running the command. Please refer to the topic to fix it at max frequency:
Nvvideoconvert issue, nvvideoconvert in DS4 is better than Ds5? - #3 by DaneLLL