I am unable to connect the Giant Recon HL900 and Varia UTL510 to my Edge 830 at the same time. The light network fails to form. Connecting the devices individually works but the experience with the HL900 is intermittent, where sometimes the lighting controls don't appear on the Light Network widget.
I have tried pairing the HL900 with my Vivoactive 4. Sometimes I can control the lights even though it says the light is disconnected.
I found a similar historic post re: older Varia unit and 520+ so it appears this issue hasn't been fixed.
While this may be an issue with the HL900, I thought it would be worthwhile posting here for workarounds and to understand whether this is a Garmin light network limitation.