@Marvin_S 

I May be having similar issues.  My IoT network was rock solid before the last update.  Since then it is a struggle to keep my devices online.  Is the update coming out soon or could I try the beta as well?  (3 X20 and 2m5 with gigabit backhaul)

  @ARGamingPK1 My issue was fixed by installing a beta firmware supplied by the TP-Link support team. It's been over a week, and I haven't experienced any connection drops on my 2.4 GHz network. I think the issue was mainly related to the fact that the Deco nodes were using the 2.4 GHz network as a backhaul in addition to the 5 GHz and 6 GHz bands. With the beta firmware, they've included a setting that can disable the 2.4 GHz band from acting as a backhaul, and this fixed my issues. However, I'm still stuck with the 40 MHz channel width on the 2.4 GHz network. Hopefully, they will include this adjustment capability in the future, as they've already done on models like the BE63, BE65, and BE85.

  @Marvin_S   I am also having these issues. My situation is this:

1: 4 Deco X20's covering about 2500 sf.

2: Broadcasting a main network, guest network, and IoT network. Had to turn on 5ghz band on the IoT network in order to connect my phone to it to add smart devices. (The phone won't connect when it is 2.4ghz only, and even with 5ghz is often showing "no internet connection" which doesn't help when I'm trying to add 2.4ghz smart devices to the IoT network by having my phone run the set up process from that network). Forced to turn on 5ghz on the IoT network defeats the purpose of an IoT network which is supposed to only broadcast 2.4ghz so as not to confuse primitive smart devices that can't connect to 5ghz.

3: Have about 25 devices on the main network, and another 35 smart devices on the IoT network.

4: Smart devices have been dropping off line for several weeks every couple hours. Multiple attempts to reboot or to "optimize network" to change the channel were successful about half the time, but it would still take several minutes for all smart devices to reconnect and then they would just get kicked off again after an hour or two.

5: Have multiple satalite deco's dropping off line randomly. It is not due to placement, or connection strength, and seems to be random.

6: Yesterday I finally pulled the power plug on the main deco and did a hard reboot. Everything booted up swimmingly and all devices connected and stayed connected for the next 20 hours or so which is longer than I've been able to keep them online for weeks now. But this morning they were dropping off again.

I'm getting pretty frustrated, 60 wifi devices (40 on 2.4ghz and 20 on 5ghz) shouldn't be causing all these problems.

I'm willing to upgrade the main deco to an X60 if that would help. I would like to stick with TP-link if I can and not switch to another mesh system all together because other than these problems I've been pretty happy. But as anyone knows, a smart home is only convenient when the network is stable. If the network can't handle the devices, the smart home becomes a living nightmare.

Thanks for any help or advice.

Edit/Update:

After posting this two weeks ago and no response, I've continued to have the same issues as other posters on this page. I've given up and bought a Orbi 770 series, which so far is not causing any of these issues. Much more expensive, so was sad to move away from Deco, but as I stated above, a smart home only works well if the network that supports it can handle it, otherwise it is an absolute nightmare. I spent 100s of hours troubleshooting the deco system and finally had to give up. I'll be listing my 4 X20's on facebook marketplace. Sorry it came to this.

  @DWiebe Add me to this list. 8 XE75 pro's, all wired backhaul, XE50-POE wired backhaul, and an X50-Outdoor wired (450sqm house and some garden area, solid concrete walls so signal penetration through them is bad). About a month ago, I think, my 2.4ghz network just stopped working consistently. 

I tried to set up the IoT network, but that is equally unstable, not to mention it doesn't let my phone connect to it at all most of the time, and when it does rarely connect for setting up smart devices, it says it has no internet connection. 

This is quite an expensive set up to only be functional for wired devices and 5ghz...

 These TP-Link folks need be looking at the Sonos case study on how to lose the faith of all your faithful invested customers and get the CEO fired.  By not solving this major issue and getting a fix released they are on step 1 of his exit plan.  Painful way to go out. Fix this get the firmware update released ASAP.