Well it has worked perfectly with 150-200 mbit speeds for a year. After the firmware update nothing works properly.

Are you guys with issues using wired or wireless backhaul? I'm all wired and so far, no issues.

The only thing I also changed was to set a custom QOS and set everything to high.

Hopefully the TPLINK rep is onto this as there is clearly an issue!

Wired back-haul for me. Worked flawlessly for a year and then this...

Couple of things to try perhaps (based on things I tried to fix Orbi reliability issues)

1. Assuming it's wireless devices with a problem, make sure the devices forget the wireless network and then rejoins with re-authentication.

2. set up the guest network and see if devices connect to that. perhaps also just set guest network to 2.4 or 5ghz band.

3. set up fixed ip addresses.

All very time consuming, but that's mesh networks for you!

Wired backhaul here and just running in AP mode. I take back what I said about beamforming. This system is effing garbage. I'll be sure to tell everyone I know never to buy another TP Link product ever. 

After more time than I care to admit, I have found my issue.  

Turning off "Mesh Technology" on every device exhibiting strange behavior seems to have fixed all of my issues.  (Device list, click each device, click the pencil, toggle "mesh technology" off)

There seems to be no documentation on what this toggle does, although I am sure it has something to do with TP-Link's implementation of 802.11r

I have yet to see any negative effects running this toggled off for most of my devices, but honestly it's hard to tell.

Here's the list of things this fixed:

1.) Chromecast Discovery flakyness has ceased (devices disappearing from the Wifi network but not the wired network)

2.) Inability for certain Wifi devices to connect to the AP

3.) Hiccups in connectivity for certain devices

It sure would be nice if this forum was visited by technical support every now and then.  It seems a little ridiculous to have this if nobody is going to help users who are having issues and it's going to do nothing more than sow more discontent.  I'm inclined to throw this entire system in the garbage at this point.

I solved my problem here.

Just fixed Bandwidth into QOS!

I have fiber connection 300down/100up. 

Fixed Bandwidth and reboot all decos.

Arrrrgh, I am so pissed off.

Cast discovery is acting up again.  This updated completely wrecked my network and there's no way out of this. 

Mine after firmware update lastnight all went wrong that I have to disconnect everything and need to reset my main deco... even after reset it is not broadcasting the SSID. Now I am stuck with my provider's router/modem. I can't use the 3 Deco m5. Even tp-link support can't help me earlier.