CM400 &smart tv, when channel changing, image focus delay

   Hello. 1st timer...SCHWING! Ever since COMCAST upgraded my internet performance package from25Mb to 50 Mb, my Samsung smart tv (mfd. 2107) has an image focus delay (3-9 seconds )when changing from one TV plus channel to another. My WiFi router (BELKIN N600) is hard wired to the desktop CM400 NEGEAR modem, and the modem is hard wired to the Tv at a (physical) distance of approx. 11 feet, w/o obstructions, using a 25' cable along the floor baseboards. Samsung has remotely performed a diagnostic check on the Tv & says it is working properly. COMCAST says that my NETGEAR CM400 is 'not supported.' Previous to the COMCAST upgrade, I did not notice any focus delay when changing channels. I welcome any input from the community. COMCAST could not/would not make (or suggest) any cause. The hard wire connection between the BELKIN WiFi router & the Tv is the only peripheral connection. I do not use any other 'wireless' devices such as a printer, scanner etc.  My primary Tv watching is done with Amazon Prime video. Once again, there was NOT any out of focus issue when changing from one channel to another before the COMCAST upgrade. I do not see any rest button on the CM400, however there is a pinhole on the back panel located about midway up. I am a lightweight surfer. According to COMCAST, I use approx. 1/3 of the national average of data. Would anyone care to comment? I am obliged for any input. Thank You, dinosoar.