@PocoPirate I'm having a similar problem but I don't think I updated my firmware recently (could have been auto-update though).

Have you tried reverting to an older firmware?  You can find the files here: https://www.tp-link.com/us/support/download/deco-x5000/#Firmware

This warning is given for this version: "This version upgrade is irreversible and you cannot downgrade to the previous firmware after the upgrade."

So I didn't try.

Is it still possible to downgrade? Tech support didn't offer that as a solution.

  @PocoPirate Sorry, I don't think it is possible to downgrade.  The BE11000 has different firmware which allows you to downgrade so I thought that might have been an option for you.

I tried getting some logs yesterday but I don't understand them that well.  Something to do with wireless client associate or dissociate.  Hopefully a fix comes soon otherwise I'll have to go with a different access point.

  @alams154  Check your DHCP setting.   For whatever reason, on my units, DHCP defaults to ENABLED when switching to Access Point mode.  This was the case when I bought the units and still the case with the latest firmware.  Clients need to get IP addresses from the Router (not the Access Point) for an access point to function correctly.   Make sure DHCP is DISABLED. 

  @PocoPirate Yep, I've already tried messing with the smart DHCP setting both enabled and disabled.  The smart DHCP enabled seems to partially work since it gives an IP address in the range of the router DHCP but gives the wrong gateway (sets the access point as the gateway).  With smart DHCP disabled, the router is able to see and hand out the correct IP address via the DHCP server but is unable to ping any of the devices or the access point itself.

I don't know how similar your problem is to mine, but I can't even access the Deco app or Deco webpage if I am not connected wirelessly to the access point when in access point mode.  Wired devices to the Deco seem to have a problem receiving an IP from the router and cannot access the Deco webpage.

If you are able to access the Deco webpage, you can find logs in the advanced section.

  @alams154   For my units, the app has a settting "Ignore Ping from WAN" which is enabled by default.  It shows up under the "Internet Connection" option.  I would assume that disabling it would solve your ping issue.  I've never messed with it.

I'm not sure about accessing the app if not connected wirelessly to the access point as I can't get the Access Point to function (it's a brick as soon as Access Point mode is enabled). 

Right now I have two wireless networks running.   My old WiFi system (and associated hardwired devices) and my broken Deco units running in Router mode with a different SSID. I am able to access the Deco units from the app when connected to my old WiFi system.

When my Deco did function as an Access Point, I connected my hardwired devices upstream of the Deco unit.  (My hardwired devices plug into a separate Switch.  The Switch and the main Deco unit plug into the Router.)  I don't remember any problems getting an IP address, but wiring upstream definitely improved performance.  I didn't mess with it too much as my arrangement work well.

I haven't accessed the "Deco webpage".  What is that?  Is that something I can access by pointing my browser to the IP address of my Deco?

I'm hoping to have some time to do more debugging later today.

  @PocoPirate  I think "Ignore Ping from WAN" is for router mode only.  My Decos don't respond to pings even in access point mode.  The main thing I'm understanding for the ping attempt is that the Decos still have some sort of firewall up even though they are in AP mode.  AP mode usually works for a couple seconds after restarting the Deco but stops working pretty soon after.

I am also able to access the Decos from the app when in router mode.  Router mode works but I need AP mode since I can't have my wireless devices behind a firewall (I need direct IP access from one of my hardwired devices).

The Deco webpage is hosted by the Deco units and allows you to see some information about your Deco "network" and you can access it at the IP the router assigns to the Deco.

  @alams154  As it turns out, there is a way to downgrade.  See the help article How to use firmware recovery if the Deco become brick | TP-Link.

I downgraded to 1.2.9 (and setting "Smart DHCP" to Disabled), I am back up and running.

Hopefully, someone at TP-Link Deco will figure out how to properly implement Access Point mode in the very near future.