packet loss with gstreamer broadcast in spite of low bitrate

I’m trying to broadcast HD videos from gstreamer with rtp to mediasoup on windows.
but, packet loss often occurs in spite of bitrate is 1000kbps though.

When I set bitrate to 350kbps, packet loss does’nt occurs.
but it’s not enough video quality .

Does anybody know what’s the problem ?

I attach my gstreamer command.

gst-launch-1.0 --eos-on-shutdown rtpbin name=rtpbin rtp-profile=avpf mfvideosrc device-index=1 ! 
queue max-size-buffers=500 min-threshold-time=66000000 ! videoconvert ! videorate ! videoscale ! 
video/x-raw,width=1280,height=720,framerate=15/1 ! mfh264enc bitrate=1000 quality-vs-speed=0 rc-
mode=1 low-latency=TRUE qp=51 ! rtph264pay ssrc=22222222 pt=102 aggregate-mode=0 ! 
rtpbin.send_rtp_sink_0 rtpbin.send_rtp_src_0 ! udpsink bind-address= host= bind-
port=10200 port=52338 buffer-size=1000000 rtpbin.send_rtcp_src_0 ! udpsink bind-address= 
host= bind-port=10300 sync=false async=false buffer-size=1000000 udpsrc port=18791 ! 

my environment is below.

gstreamer v1.22.4.
mediasoup v3.12.10.
mediasoup-client v3.6.51.