Getting lag spikes while gaming.

 I am using the Xfinity Arris TG4482A modem with a Netgear Nighthawk wireless mesh router system. For months this combo worked great. Then, about a week ago, all of the sudden, I started to get lag spikes that were more noticeable while gaming. These spikes are happening to the point that multiplayer games are sometimes unplayable. The spikes happened with both wifi and ethernet connected devices. It doesn't seem to matter what time of day, the spikes still happen anytime. I have tried power cycling the modem, router and the satellites multiple times with no luck. I have tried changing the modem to "Bridge Mode" and this only made the internet randomly cut out along with the lag spikes. I have the router plugged into the first port so that shouldn't be the issue for the loss of internet connection. After all of this, I contacted Support and the Support technician ran through all of these same troubleshooting steps. However, this time we tried turning off the router and only connecting to the modem. This actually did work. The lag spikes went away. The problem is that I need my Netgear wireless mesh system going to have better wifi coverage in my house. The wifi, from the modem only does, not work as well. The Support Technician pretty much implied that it wasn't an issue with the modem and offered to send out a technician. I declined because I wasn't sure if I would be charged for that plus, I wanted to do a little more troubleshooting. I happened to have another brand new, never used Netgear Nighthawk wireless mesh router of the same model, that I wanted to try. I powered off all the equipment and setup the new Netgear router. Then, I powered on the modem and all the satellites. Tried a game and.... same issue, lag spikes and disconnects. I even tried powering off all the satellites to make sure those weren't the problem but still the same issues. I power cycled everything a few more times, powering on the modem first, and still the same issues. I then found that the splitter outside can sometimes cause this issue when it's old so I replaced the cable splitter with a brand new one but that didn't help. I then tried swapping the patch cable from the modem to the router and still the same issue. I also made sure the coaxial cable was tight on the modem and the wall and it was.  I then decided to disable "Bridge Mode" and this helped with the disconnects but the lag spikes are still there. I then verified that the modem alone does not have lag spikes and sure enough, no lag spikes when connecting directly to the modem. Again, I need to be able to use my wireless mesh system though. I wanted to check here to see if this modem has any known issues. I really feel like it's the modem and I'd like to swap it out. It's almost like it's overloading when I connect the router to it. Any help would be appreciated.