From what I've noticed it moves one of my smart devices to the closest deco unit to it, for some reason it wants to connect to the ground floor deco and not the unit about 6 inches away from it. 

But I would love to know what else it does, seems like just a marketting feature.

@AnotherMJB I'm wondering the same thing. I think it probably changes channels as that's the only feature that was missing from the firmware previously.

@AnotherMJB From what I have observed, running the Network Optimization can come back and say that a channel is congested. Allowing the optimizer to Fix the issue results in it selecting a new channel. So far, I've only seen it come back saying congestion on the 5GHz channel where it switched from ch36 to ch44. However, it appears that if you reboot the Decos, this channel selection is lost. After rebooting my Decos, I found that they went from ch2 (2.4GHz) and ch 44(5GHz) to ch10 (2.4GHz) and ch48 (5GHz) which then resulted in my home network becoming completely unstable!

Prior to updating to this Firmware release, my network was stable and running great. Since upgrading on Friday night, my network has had periods of stability, but then become unstable at other times. I wish there was a way to go back to the previous release...

@navigator48 I've noticed the instability too after the update. We should be allowed to change channels manually as I'm not sure how it detects the "congestion" in the first place. I assume it's measuring congestion based on where the deco units are. However it's more important to measure the best channel based on where my most used device is located. I live in a condo so the living room may not be congested but there are neighbouring Wi-Fi signals making the channels congested in the bedroom. 

@Ikkie I spent 3 days trying to get my 3 Deco M5 (V3) units working correctly with the 1.5.1 / 201022 build firmware. I was never able to - which is really bad with me and my wife working from home!

Ultimately, I reverted to the 1.4.9 / 20200924 build. Neither the web UI, nor the iOS app will let you downgrade. But, I found an article telling how to use TFTP and boot the Decos into restore mode and that worked. Now that I'm back to 1.4.9 everything is working properly again. I did make one other discovery... Using PingPlotter, I was seeing up to 20% packet loss over the WiFi. By turning off Beam Forming and rebooting, all of the packet loss stopped. Beam Forming is supposed to provide the strongest signal to devices. But, in my network's case, it was doing the exact opposite.

Now that the network is stable again, it will be a long time before I do anything other than moving the Decos to optimize coverage. It was a huge hassle to recover from this update not working! I'm going to be very skeptical of any future Firmware updates issued by TP-Link.

@navigator48 Sorry you had to go through that. My two deco setup still works okay. Just that my phone kept telling me I had no Internet on WiFi several times. After using the network optimization feature a few times, it now seems to be working better. I've always turned on beam forming but don't really have a clue what it really does. 

I have had unstable connection since this update too. Pages take too long to load. I 've tried to restore Deco M5, it seemed to work at the beginning but the problem came back soon. I ve already checked with ISP provider, restored my ISP router, and when I connect directly to the router it works normal. Now seeing this thread I am pretty sure the problem is with this firmware. I hope TP Link fixes this soon. Meanwhile is there a temporary fix to this? I couldn't find the TFTP solution mentioned to downgrade and am afraid to brick it anyway.

@FeliA Here is the article I used to downgrade the firmware. I hope this helps you as well...

https://www.tp-link.com/us/support/faq/2958/

@navigator48 Thank you!

@AnotherMJB I'm searching for any documentation on the new features, including "Network Optimization" and "Ignore Ping from WAN"...  I someone finds it, please share!

When I first pushed the update, it seemed like a mess.  For example, none of my Echo Gen3s would connect (though my Echo Flexes seemed fine).  Unfortuately, it was the day before Thanksgiving and I had a ton of preparation to do... after screwing around with it for about an hour, I had to just walk away and figure it out later.

This turned out to be a good thing, since everything right itself.  I'm not having any connection or performance issues.  I did reboot things about a thousand times and run the Network Optimization, though Lord knows if it made any difference.  I have five M5s throughout the house.  Maybe just give it some time.