Do you use the latest FW?
When you lost connection, how can you get them reconnected? restart?
Try to unplug all the RE units to see whether it will lose connection frequently.
For your case, it's better send email to support@tp-link.com directly with your detailed information to get further help from tech support.

Bottom line -- they appear to work for a little while, but don't do so consistently enough to provide a reliable service.

I've got 3 Deco M5s running in Access Point mode and this should be easy peasy -- no policies, no firewall stuff, just WiFi and the mesh connectivity to make a bridged network.
But they don't stay in "green" mode for long, with some or all of them going into "blinking red" mode at random intervals.

The diagnostics to analyze why they are failing are non-existent. When they aren't working the iPhone app generally says "We couldn't find Deco.". And even says so often when the light is green. Why doesn't it try to use Bluetooth to contact them like it uses for setup when it can't get to the cloud server?

If you catch it when they are working you get "All Decos are online; Deco is working well." but you can't get it to tell you why it was just blinking red a few minutes ago. And sometimes when "All Decos are online" it only shows 2 out of 3 of them.

This is with the latest firmware, 1.1.6, which apparently hasn't been updated since before Thanksgiving -- guess the programmers at TP-Link are all working on newer, more important projects.

As an example, my VDSL2 modem/router saw the ethernet port to the Deco go down 4 times in about 2 minutes, then come back up 3 seconds after failing each time (the light stays blinking red for much longer than just the 3 seconds). And I'm not moving the Decos or changing any wired connections -- you'd think once they got the "mesh stuff" working they'd just stick with it.

I wish they'd just post the software on Github so people who know what they're doing could just fix it themselves. Or at least push diagnostics up to the cloud (when things seem to be working) where we could look at them through a TP-Link support web page.

If you enjoy going around your house pulling the power plugs and putting them back in all day to reset the software then this is the networking solution for you.

Is your Deco unit that is connected to your modem setup as 'Router' mode? The rest can be in AP mode.

Have you tried chaning the place of the deco units? try to change the places.
What's the LAN ip address of your main router?
If it's 192.168.0.1, you can try to change it into another subnet, such as 192.168.10.1

rajivhifi wrote

Is your Deco unit that is connected to your modem setup as 'Router' mode? The rest can be in AP mode.

All are in AP mode. One connects to the the Frontier VDSL modem/router (ethernet cable) which handles all the "router stuff" like DHCP, etc. All the Decos do get their IP addresses from the VDSL router and they do do bridging sometimes.