I have had the Deco s4 (Main with 2 satellites) for a while now but recently I've noticed that it consistently loses maximum speed. 

I pay for 500mb/s through Virgin in the UK however the majority of the time my Deco only outputs around 60/80 MB/s over both Wifi and my PC which is wired via Deco with Ethernet.

Rebooting the Main Deco brings the speeds right back up to 400+MB/s but over time (I've not tested how long but certainly within a day or 2) this dips back down to the 80MB/s range.

I don't have any devices set to priority and I have manually adjusted the limits to 1000MB/s but it hasn't helped. 

I don't think it is a Virgin throttling at peak times issue as the speed tests ever go up above the 80 MB/s limit once it falls but instantly comes back after a reboot.

Any ideas?