I have CGM4140COM gateway and a smart home device which have been working fine till November 2018 and all of sudden from December 2018, it started having WiFi connectivity issues. My other smartphone and Laptop devices seem to be working fine and they are not having any issues but just this smart home device. My gateway had CGM4140COM_3.1p28s1_PROD_sey firmware on it in Feb 2019 and now it has CGM4140COM_3.3p15s1_PROD_sey firmware on it. Unfortunately, I don't know which software it was running prior to Feb 2019(or Dec 2018). So does anyone have any idea on why this could be happening with the latest software push?
Since it's the only device that seems to be affected, I'd check troubleshooting instructions for that device, preferably on their support site, to see if someone's found the problem.
The firmware on mine is CGM4140COM_3.3p13s1_PROD_sey slightly different to yours unless it was a typo. Not noticed any problems with my devices. Have you tried resetting the smart device?
I was having VPN connection problems with the XB6, upgraded to an XB3/Arris TG1682G and it resolved the problem. Without more detail that's a shot in the dark.
FWIW, there have been two different makes and model numbers of the XB6 gateway device for Comcast. They are ArrisTG3482G, and the Technicolor CGM4140COM.
I tried resetting(rebooting/power-cycling) the smart device number of times but that's not helping(also tried resetting router number of times but that's not helping either). I also tried to take follow-up with the smart device company itself and they are saying that issue is from the router side and specific XB6 models' latest firmware update caused this issue. So if I change that to any other router model then the issue is going away completely. So for sure, this issue looks like tightly coupled with the Comcast router XB6 model and to be exact with the latest software update because before that same model was working quite well for a long time.
Wouldn't that be a downgrade, since that is a DOCSIS 3.0 device that you 'upgraded' to, from a DOCSIS 3.1 device? Lower max speeds, but for what its worth, if it fixes your problem and you are happy, then it was a good upgrade.