In this case please just confirm one thing since you mentioned that you are using separate router connected to the modem for wifi, have you enable bridge mode on G36 before connecting mesh system. Because without enabling bridge mode if you use separate router for wifi it will cause interference so you will be getting these type of error message on the devices using wifi.
I kept one 2.4GHz band up and running on the G36 in its room so that I could keep remote access available, and then the rest of mesh wi-fi is spread out in the house utilizing the 5 & 6GHz bands.
If you are connecting G36 with the mesh system, I would suggest enabling bridge mode to avoid interference.
http://arris.force.com/consumers/articles/General_FAQs/G34-G36-Bridge-Mode-Setup
That is what i did originally, but then i discovered that any time i needed to access my G36, I wasn't allowed remote access so I had to go grab a computer and dig up a cable to connect with it. So, i dropped the 2.4G radio from my mesh system, and then disabled the radios using the higher frequencies on the G36, and used only the highest three bands for the mesh system, so there's no conflict on any of the same channels, and i still have remote access to my G36.