Hello,
Please try it with VP8 priority to see if that is related to H.264 support. Some devices may not support H.264.
In WCS_HOME/conf/flashphoner.properties place vp8 before h264
codecs =opus,alaw,ulaw,g729,speex16,g722,mpeg4-generic,telephone-event,vp8,h264,flv,mpv
and restart the WCS.