I have a 4 disc BT Whole Home Wifi setup and since switching to this any time I cast anything to my Chromecast there is an audio delay with the video. So if someone speaks on the video, the audio follows about 1 - 2 secs later. I never had this just running off the router WiFi previously.
I've updated all firmwares etc and still the problem persists. I even bought a v3 Chromecast that arrived yesterday, set it up and updated it and the sdame issue is present on this one.
Spoke to BT tech support and they just advised changing the chanels the Wifi uses to 1 and 40 but this made no differences either.