@Kwiatek 

When this happens next time, check "Show Map" page of Deco app to see how Deco units connect to each other. Deco app may not update that info in real time, so first check "Show List" to see that wired Satellite Deco is reported on WiFi backhaul, like in example below, then make screenshot of both pages and post them here.

Example of "Show List:"

Example of "Show Map:"

  @Kwiatek The only way I found to do it was to power the Decos up one by one.  If they all came on simultaneously, then one or two of them would revert to WiFi backhaul and be slow, also affecting the data rate available in the vicinity of the first leg of the WiFi backhaul mesh node.  I wish there was a way to disable WiFi backhaul as after a power cut, I have to go and switch off Decos and then power up each one until the green light shows on the front.

  @bouncingboffin 

You can see in Deco app what type of backhaul Satellite Deco is using. In example I provided, Bedroom is on WiFi backhaul, while Study and Office are on Ethernet backhaul.

Ethernet backhaul takes priority over WiFi backhaul. If Satellite Deco runs on WiFi backhaul, it means it can't use Ethernet backhaul. Having switch to turn WiFi backhaul off won't help, Satellite Deco will just stay disconnected.

Unplug Ethernet cable from Satellite Deco on Ethernet backhaul and it will switch to WiFi. Plug Ethernet cable back and Deco should almost instantly switch to Ethernet backhaul.

"Show Map" and "Show List" screenshots may help to pinpoint where the problem is. Without them not much can be done with just description you provided.

I have only a theory, that if you use PoE and multiple Deco go online simultaneously, switch can't handle spike in initial power demand and will cut off link to one/two units that draw power from it.

This is very much speculation, but if this is the case you need to bring that to Linksys support forum and also see if connecting one or few X50-PoE to their individual power supply will make that issue go away.

  @bouncingboffin Yes. Same here. Have to switch on one by one after restart. Otherwise one or two will be on wifi..

I cheked my poe switch. Only 6 to 10 watt each port is in use. It can handle 36 watt each port. Will try use powersupply and see if it fix the problem