assertion error when handling sink event

I am working on a PoC iOS project where i try stream the camera-buffer using appsrc to a server (using test-record example from gst-rtsp-server).

My current pipeline is as following:

appsrc name=appsrc block=true is-live=1 do-timestamp=1 format=3 stream-type=0 min-latency=0 max-latency=50 !
        rawvideoparse width=720 height=1280 format=nv12 !
        x264enc tune=zerolatency speed-preset=ultrafast !
        rtspclientsink location=rtsp://127.0.0.127:8554/test latency=0

I then push the buffer to appsrc and test-record opens a window showing the stream but it crashes within about 30 seconds most of the time:

ERROR:gstrtpulpfecdec.c:487:gst_rtp_ulpfec_dec_handle_sink_event: assertion failed: (self->have_caps_ssrc)
Bail out! ERROR:gstrtpulpfecdec.c:487:gst_rtp_ulpfec_dec_handle_sink_event: assertion failed: (self->have_caps_ssrc)

I am not sure if I can do something in my end to fix this.