We have tested your server with this demo page:
https://35.163.225.113:8888/demo2/webrtc-as-rtmp-re-publishing
It works fine in our tests. Bitrate is 2Mbps.
You can also check combination of settings:
codecs=opus,alaw,ulaw,g729,speex16,g722,mpeg4-generic,telephone-event,h264,vp8,flv,mpv
or...