@David-TP Thank you David! The 3rd party device is a Sony Bravia KDL-40EX1 digital TV consisting of a TV screen and media box connected through a wireless connection. I was wrong about the bandwidth,...

My Deco M5 mesh interferes with a 3rd party local 2,4 GHz connection (not wi-fi). Deco is set to use 'only 5 Ghz', and I have run the interference tool in the Deco app, but still creates intermittent...