I must be doing something wrong. Went through setup fine, updated firmware and initially, for at least the first 48 hours, everyting worked perfectly. I was singing in the rain! All areas of the house and immediate area outside had a strong WiFi signal. 

Then, we started getting frequent drops. They usually only lasted for 5-10 seconds then it gradually increased in frequency and duration over the next 3 weeks. Devices wired directly to the gateway had no issues. Devices wired via gigabit switch to the gateway had no issues. Power-cycling the Xfinity Gateway and main Deco seemed to get things working again but the issue keeps returning. Network optimization in the Deco app alwasy says everything is great but that is clearly not the case.

I reset the Deco's and designated a different unit as the main puck, had same exact issue started happening. I rewired so the only thing plugged into the modem was the main Deco unit which was also output to the switch so everything internet connected went through the Deco system. Now all devices had issues. Ugh!

I contacted both Xfinity and then TP-Link support.

Xfinity claimed no issues and to confirm, if I plugged my laptop into the gateway, internet was fine while devices connected via the Deco were not connecting.

TP-link support suggested switching to AP mode which I did and this was even worse. They did not warn me about backhaul and the need to wire the 2nd & 3rd Deco units which seems to defeat the purpose of having mesh WIFI in areas with weak signals.

Following other forum tips, I disabled DHCP on the Xfinity Gateway figuring there was some double NAT'ing going on causing IP conflicts. That didn't help. I put the gateway in bridge mode which is apparently a big mistake when using an Xfinity-"rented" modem. That rendered me totally web-less and unable to access the gateway's UI thus unable to switch it back. Had to call to have Xfinity reset it from their end.

I set everything back how it was originally, went back throguh the Deco setup from scratch again and have the same issue. I did also notice that the Deco unit that's visible in the living room occassionally flashes red LED. They are all usually off or show green occassionally otherwise.

So, all that being said and done, I am left with the same issue, frequent, although brief, connection drops which are too disruptive for fmaily members to work or do schoolwork online for more than brief stints since they get logged off when the internet drops. I am about to send them back for a refund and try a different brand of mesh system like Netgear, Ubiquiti or sometihng. This is very frustrating because these are reasonably priced and get great reviews. 

Any advice would be greatly appreciated.