4 years with an AC4000 was fantastic. Everything just connected and worked. My experience with the BE550 has been problematic. 

I finally got everything connected except my only smart-plug. The HS105 wouldn't connect so last week I bought a KP115, same issue. 

I carried over all the settings from the AC4000: SSIDs and passwords. Of course I've reset the network hardware several times and tried the KP115 setup with it less that 4 feet away from the BE550. The SSIDs and passwords are the same for all of the bands. I've tried MLO on and off. 

I've tried all the suggestions that I could find on the web, most of which were nonsense and gone through the setup in the manual. 

Since I've not yet gotten rid of the TP-Link WiFi gear, I'm tempted to just sell the BE550 on eBay and go back to the AC4000. I appreciate the extra speed of the BE500 as I send large files (50-100MB) up and down to Adobe servers. 

Other devices on the network: Ring Doorbell (required all the bands to have the same SSID and password), RE300 Range Extender, two iPhones, iPad, iMac, MacBook, Samsung TV and (no longer used) AC300 with Windows. Also had several Android devices which I've since sold, all worked fine. 

Note that the Ring Doorbell requires the same 2.4 GHz band and one of the Android devices used the 5 GHz band so I know that all the bands work. 

Suggestions appreciated, 

Bill