So, either roll you install back to 0.84.3 in HASS OR roll your Harmony back to 4.15.206, so they either both use websockets or both use XMPP.
What I did was to download the 0.84.3 zip file https://github.com/home-assistant/home-assistant/archive/0.84.3.zip and copy the “harmony.py” file from 0.84.3 to my /home/homeassistant/.homeassistant/custom_components/remote/ directory (and restart HASS) so I’m still on 0.84.6 but running the harmony component from 0.84.3.