@karikala,

Are you testing all of these devices in the same room? If so there may be too much interference for the deco to correctly optimize and select its channels. It is always recommended to set up the units in their end location if possible.

Otherwise, how is your network configured? Are you using a wired or wireless backhaul?

Try testing the speed on the various Deco Units with an ethernet connection, rather than wifi. This way you can see if the router is receiving the full signal, or if there is an incompatibility somewhere else.