I am stuck on a similar problem.
I have 2 pipelines.
The first one is: filesrc → tsdemux → h264parse → rtph264pay → appsink.
the other one is: appsrc → identity (for debugging purposes) → webrtcbin
In the logs I see only one line from identity input:
4100000000 (0x7977ec002ce8): 80 60 4b 07 90 f6 c2 8a b9 f5 be a9 09 10 .`K…
and when I print the buffer size of appsrc (the element before identity) I see its only getting bigger (means its not flowing out of appsrc).
Before I split the pipeline into 2 (with appsink and appsrc) I had one pipeline (rtph264pay was linked with webrtcbin) and it worked fine.
Did you manage to solve this?