Switched from old Orbi RBR50 mesh as I got a new 1Gbps fibre connection. 

Setup:

- 2 bedroom apartment with solid walls across each room. In-wall ethernet wiring for each room. Living room has main router. 

- Deco X75 Pro is the main router with User/Pwd PPPoE connection to cable provider

- TP Link TL-SG105 5 port gigabit switch connects Deco X75 main router to in-wall wiring connection points

- One each Deco X75 in each of the bedrooms connected by Ethernet backhaul as confirmed by deco app

- All Cat 6/6e cables

When I setup: I was getting 900Mbps on the phones and lower on macbook etc. 

After a few days, the entire line has degraded. I am right next to the router in my guest bedroom router and all devices are down to 250mbps. 

In addition, my living room TV connects to bedroom router over living room, and I am unable to switch it over to the living room. Issue - screen mirroring stutters in this current setting. That was never the case with my Orbi. 

Thoughts on what services I should turn on, or turn off?