Frequent stops in communication with game servers even with 800 mbps connection

Hi, We have 800 mbps Xfinity to our home. We have latest Xfinity modem/router. If just one PC (with latest Intel processor) is used to play Rocket League or Call of Duty (COD) communication with game server is stopped for a few seconds every 5 to 30 minutes. The other players in the game that are not in our house don't have this problem, so I think it is a Xfinity problem, not a game server problem. There is never a time when there is no communication loss. If two PCs in our house are playing Rocket League or COD then both PCs lose communication with server so frequently that these games are unplayable. The other players not in our house don't have a problem. Initially the two PCs in our house used for online games were connected to a Xfinity Pod with a cat6 cable. Xfinity speed test results were about 500 mbps. Then we wired an old switch with cat6 cable to the Xfinity router and cat6 cable to the PCs. Speed test results were 800 mbps but the same problems remained. The measured gateway speed is about 910 mbps. What can we do to fix the problem with games? Thanks very much! Regards, Bill