I have two modem routers with my isp.

Where i live reception has always been poor (about 3-4mbps) for my 4g signal,  but recently i found that the very best signal is in the roof which has a better line of sight to the mast. This gives around 25 mbps.

With Deco i no longer need two of them around my house, so ive  removed one router completely  and connected the other to the deco m5. Two additional Deco nodes have been positioned 

Initially, all seemed well with good speed and signal around the house approx. 15 mbps.

However, over the last few days the speed has gradually reduced and now it seems to have levelled out at a consistent 5mbps download which is not much different to what we had without repositioning the router in the roof AND without  Deco.

As a test, i reconnected the second modem router but independent of the Deco and it gave readings of 26 mbps..!?

 Figuring it was the router that was the problem i switched the routers around on the Deco... But no change the speed remained at 5mbps.

So this morning i have run the Deco speed test which reports 26 mbps up and down.

I do an ookla speedtest for the clients on the Deco network and it reports 5mbps download / 6 mbps upload..   

I still have the second router connected independently of the Deco...a speed test of that reports 25 mbps.... And the signal is good enough around the rest of my house compared to what i am getting with Deco.

So why is Deco reducing the speed i am getting overall? ...i may have to return because on the face of it , Deco is not bringing me any benefit whatsoever particularly if it is reducing bandwidth to my house.  

Any help/ comments would be appreciated, thank you.