Regarding latest firmware version or any updates for Firmware you have reach out to your internet service provider only. 
Since you mentioned that you are using bridge mode on G36 do you have separate router connected to the modem for wifi?

I am using bridge mode with an Eero router. I don’t know if that avoids connection issues. I’ll be monitoring to determine that.

And I still don’t understand the position that a problem with firmware requires Comcast to push the upgrade.  Do you have any documents from Xfinity Comcast that state that?  It doesn’t sound right.

The issue is “inside the box.”  It should be correctible by the box maker. It doesn’t sound logical --  would Apple require Verizon or T-M0bile to push a software fix on the phone?  

Normally, ARRIS develops the software update and makes it available to service providers.  The service providers qualify, test, and distribute the software update to devices on their network.  ARRIS has limited control or visibility on distribution by the service providers.

The thing doesn't work and Motorola's works just fine. The Comcast tech on site said he says there is a problem with the G36 working in certain Comcast areas. He sees it all the time. Looking at the Amazon reviews and a quick Google search reveals this is a common problem. The Comcast tech told me to buy a Motorola, and I did. It works great and was half the price. I got a new G36 from Arris, they wanted me to return the old one, and once I got it, I sold it on Ebay. Arris products don't work as advertised, and they never made it right.