Apple 4K TV & AT&T Fiber 1000 Mbps Internet

I have 3 Apple 4K TV boxes hardwired using Ethernet cables, they work with no issues. The problem I am having is that when they are hardwired, my WiFi speeds are slow, downloads pause, sometimes we lose connection. I have had AT&T to the house 3 times in 2 weeks, they replaced the router, all the cables, connections on the wall outlets, installed 2 WiFi extenders, etc...

AT&T claims that its a known issue with Apple 4K boxes causing Internet issues? When I unplug all the hardwire connections, my WiFi is super fast, with no issues. I have a new construction home, wired for fiber optics.

All Apple software is up to date.

Is there a known Apple 4K box issue? Is AT&T correct? Anybody else ever have these issues?

Im really frustrated with this. Help! Thanks in advance....