You'd have to contact the manufacturer of the TV (TCL, Sharp, Hisense, etc.) for any kind of warranty replacement. Roku doesn't make the TVs. That being said, they're probably going to point the finger back at Roku. I suspect there's some kind of incompatibility with the new router, but getting to the bottom of it won't be easy.
Is it an ISP supplied modem/router? Are you able to look into and change the settings? Do you know if you're using 2.4GHz or 5GHz?
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