@Holocron It's definitely 2.6 I have, but not sure if that's a good thing or bad thing at the moment lol. 

So here is what happened after my tech troubleshooting session last Sunday.  The tech installed a debug version of 1.2.7 so he can run some SSH commands on it. Here are the results.

1. My devices were able to connect after he did some "2.4ghz band tweaking"; he wouldn't elaborate.  Basic he manually did what network optimization is supposed to do.
2. Even though devices are connecting the app still shows them as disconnected. Tech recommended I use the individual smarthome apps to confirm if they are connected or not and not rely on the TP-Link app.
3. Not all devices stay connected, but they are quick(er) to reconnect after disconnect.
4. Changing my main network back to 2.4GHZ and 5GHZ had not affected device connectivity.

Between network instability and most of the parental controls now behind a paywall, I'm testing google wifi pro on Friday. Some of my observation. 

• The TP-Link app not reporting information reliably is a bigger issue than I realized.  Google reported one of my nodes was in an poor location although it was the same location I previously had one of my TP-Link nodes.  I just assume the TP-Link node was just better, until I remembered that some of the device that connected to that node always showed weak connection.  So most likely the TP-Link node was in a bad location despite the app showing good connections.
• The parental control features that remained, ie website blocking, also wasn't working reliably.
• Before I give up fully give up on TP-Link, I'l do a factory reset and redo my network setup
• It seems like the app is also not reliable, at least for me, and hasn't been reliable for quite some time before the firmware updates.

  @DreadKnight 

Thanks for your update. Interesting what TPLink did/didn't to to try to resolve. 

An update on my network. Everything seems to be more stable on the 1.2.9 beta firmware. I do occassionally have a dropout on a 5Ghz device, but not nearly as often as on 1.2.7/1.2.8. Of course my main connectivity issues were with my 2.4Ghz devices. These do seem to be mostly responsive now. I do have to retry from time to time to connect to those devices and once in a while they will lag a bit from a slower/unstable connection. But it's far better than before on the prior firmware versions. 

I'm still not running IOT or Guest networks. I can live without IOT, but I would like to get my Guest network up and running. I'll probably enable that and see if those problems have been resolved with 1.2.9.

Let us know how the Google Wifi testing goes. Interesting you are getting better connectivity status from Google. I will say that I noticed when switching between firmwares a couple weeks back, it was very evident that a couple of my Deco units showed a lower signal strength on 1.2.9 than on the previous versions. The actual speed and performance of them didn't change though. I didn't move any of the locations of the Deco's but they definitely showed a different singal strength between firmware versions. Not sure, but maybe 1.2.9 is more accurate?

  @xjsimon 

How does one get their hands on 1.2.9 beta? I asked support and they were not helpful. Told me to factory default all the devices and reshuffle them physically, which ain't nobody got no time for that...

This is a bit maddening though. I originally thought the issue was correlated to some of the enhanced features such as 802.1R and MIMO, but I still get 2.4GHz dropouts on my smart home devices. 

Need to stabilize this already.

So it's been a week or so since running 1.29beta and my experience is (mostly) quite good. The upgrade went off without an issue.All my IoT cameras and network generally seem a lot more stable, a lot fewer loss of network, and the throughput is good such that the devices are not complaining. I was also able to reenable most of my settings including the MIMO and other settings.

I did have some random crashes, one last night in the middle of online movie viewing (it took exactly 3 minutes to restore, and the interface/app showed the lead node down), but generally in a pretty good place. Looking to see when this new  advertised 1.9 code comes out.

Hello I have been having issues with my deco system since I set it up about 3 weeks ago. My wired backhaul will fail and then my deco's will not be able to connect to internet. If I go to the main deco and remove the Ethernet wire going from the main deco to a netgear unmanaged switch. The internet connection will come back online, but to make the wired backhaul come back I have to unplug the Ethernet wires that goes to one of the deco unit. Which then restore the wired backhaul to another deco unit. I can then plug back the Ethernet wire to the other deco unit and have a normal functioning network for about 4 days or so. I have 3 Decos XE5300 v2.6 on the latest firmware with them being in WiFi router mode. The Main Deco connects to a unmanaged Netgear switch which is wired to a patch panel sending the connections to the other two decos in different rooms. I replaced the unmanaged switch already to eliminate what I thought would be a failing port, but no luck ofc.

  @DaOfficialRolex 

Is your ISP router/modem also plugged into the unmanaged switch?  I think you need to setup the main Deco as an intermediary between ISP router/modem and the swtich.  That is how I setup my network.

MODEM/ROUTER ----> Main DECO ----> SWITCH  ----> everything else 

@DreadKnight 
My Network topology goes like this Modem ---> Main Deco/Router ---> Unmanaged Switch ---> Patch panel ---> Deco #2 & Deco #3 ---> Unmanaged Switches ---> Everything Else . I had another network failure today and earlier this week as well. I went through with a cable tester to make sure the Ethernet Wires weren't the problem. I noticed that the problem was a with certain Deco so I had switched it earlier in the week with the other deco. It was stable for a while before failing again today. So I placed the one of the unmanaged switches in front of the deco where I believe the failure is occuring