@heyigun What does that "Oto" option do?

  @heyigun 

Have you tried the "connection preference" option? When a device is first added to your network its "connection preference" is set to "Auto" meaning it can switch back and forth between the two bands. You can force the devices that you want to connect just to the 5 GHz band.

First find the mac address of the device(s) you want on the 5 GHz band once you have them

In the deco app from the Network tab click on Online Clients then use the search option to find each one of the devices using the mac addresses.

Once you find it click on it then click on connection preference and under Preferred WiFi Band change it to 5 GHz

Repeat the above steps till each device you want is on the 5 GHz band. 

  @heyigun,

the units always try to use 5 GHz for backhaul after a reboot, but if the signal is not strong enough they will automatically fall back to 2.4 GHz for stability. That explains why your speed drops when it stays on 2.4 GHz.

If possible try to place the Deco units closer together or with fewer walls/floors in between so the 5 GHz link remains stable. Also make sure they are not near big electrical devices or metal enclosures that could block the signal.

If wiring is an option you can connect the Decos with Ethernet cable and enable Ethernet backhaul - that way you always get the full gigabit speed and don’t depend on the wireless link