@TP-Link_Deco 

When i extract the upgrade tool,  Symantec is reporting that it is a threat...

I just downloaded from the official link in your message..

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Scan type: Auto-Protect Scan
Event: Risk Found!
Security risk detected: Heur.AdvML.B
File: C:\tmp\M9Plus_2.0_upgrade_tool_v1.1.0_win32\M9Plus_2.0_upgrade_tool_v1.1.0_win32.exe
Location: C:\\tmp\M9Plus_2.0_upgrade_tool_v1.1.0_win32
Computer: XXXXX
User: XXXXXX
Action taken: Pending Side Effects Analysis : Access denied
Date found: Saturday, July 4, 2020  9:39:52 PM

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anyone else face this problem?

@Agathian I have F-Secure and it didn't throw a warning.

I could see why what this utility does could be seen as risky by overly protective security suites.

You downloaden it from tp-link, right. If you don't trust their software, don't trust their hardware either, I'd say.

@Willem_3 

Here is my overdue reply/report. To make a long story short, I managed to update to 1.4.0 successfully. I would like to share the following and I hope the community, including TP, will find my feedback useful:

• I downloaded and ran the update tool on my my windows laptop. 
• I downloaded the tool from the dutch site. I had to just like many others because my country site does not offer it. Why? It beats me!
• I updated 3 M9s V2 which were configured as a mesh. No problem at all. The update was from fw 1.2.11 to 1.4.0 build 20200324 Rel 53529.
• But the 3 M9s were not sufficient to cover my house via wifi backhaul. My house is concrete-based with 2 floors each is about 400 m2. Total plot area is 900 m2. So, I was not getting a reliable wifi signal everywhere. I have some old cabling that looks ugly and I did not want to rely on it for ethernet backhaul. I wanted reliable wifi backhaul so that I can get rid of the old cables.
• To strenghten my wifi network, I made the decision to double down on the M9 and bought 3 more V2 units which were hard to find. Most of the stores in my area carry the 1.0 variants (1.0, 1.1, 1.3). I hope TP will take note of the extra headache they inadvertently created for their loyal customers.
• Why did I go for more M9s? Mainly because of the following:
  •  Apparently, the M9 loses some of its fucntionality at mesh level when combined with other "lesser" decos. I posted about this before and received replies from TP. Please correct me if I am wrong. Because there is no documentation on what functionality will be lost when adding another deco model, I went for more M9 to mitigate the functionality loss risk.
  • Not only M9. It had to be M9 V2 because I did not want to have a mesh of V1s and V2s and update them separately. The same reason was enough to avoid other deco models even if the functionality issue was made clearer.
  • Aside from some bugs, the update to fw 1.4.0 worked fine for me.
• I faced a dilemma on how to update the new M9s which were fw 1.2.11 out of the box. Option1: play it safe and remove the old/updated M9s, install the 3 new M9s, update them, then add the old M9s. Option 2: just install the new M9s to the existing mesh. I decided to go option 2 because, quite frankly, by this stage I got accustomed to taking risks.
• I successfully added the new 3 M9s (fw 1.2.11) to the existing mesh of 3 M9s (fw 1.4.0). It worked but, as expected, the new M9s did not have the 1.4.0 functionality.
• With this mesh of 6 M9 V2 of mixed fw, I ran the update tool again just like I did before. It updated the new 3 M9 successfully. I must confess that I felt as if I squeaked by a potential disaster but I wanted this done quickly.
• So, now I have 6 M9s all are fw 1.4.0.
• Good... but.... with 6 M9s, my wifi backhaul was still not reliable enough for my needs.
• My short-term need is reliable video conferencing. Long-term need is smart home support (this is why I chose the M9 to begin with). Video conferencing was not reliable. I drop off meetings 1 to 2 times per hour.
• I placed one of the M9s in a hall between my home office M9, where I video conference, and the main M9 but for some reason my office M9 insists on connecting with main M9 and 50% of the time without the 5GHz backhaul. The one in the hall was always in full 5GHz backhaul. I was patient with it and left the decos without changing locations for few days but still the office (far) deco did not want a middleman with the main deco.
• Patiently tried many tweaks to the location of the nodes but in the end still not reliable enough for my needs. Hmmmm...
• In the end, I resorted to using the old cables for ethernet backhaul. It works automatically and reliably. I now have one M9 as main with 4 M9s connected via ethernet backhaul and one M9 (the one in the hall) connected via wifi backhaul. My mesh wifi bubble covers the entire house and I feel comfortable that it will support my smart house venture.
• Had I known what I know now, I would probably have given the Samsung SmartThings mesh/smart home hub system a more serious consideration.

I hope you will find something useful in this overdue and long reply.
Regards,

@AMH thanks very helpful. I currently have 2 Deco M9 v1.0 and have returned a Deco M9 v2.0 straightaway after reading this thread. Very disappointing performance from TP-Link. Misleading actually. Selling a product as identical when it's definitely not. Not reacting to queries, promising a lot but not delivering at all. I wish I had never chosen for Deco.

Now in doubt what to do next, need another AP but don't know what to do. Maybe I'll just get rid of the v1.0s as well and switch to Samsung or Asus. What is a good alternative?

@BenH070 

If the M9s you have are performing well against your needs and you only need to expand the mesh coverage, then adding another M9 (same hw version) seems to be a logical move. Otherwise, consider other mesh systems. I have no idea about the Asus or Samsung mesh systems but I believe this is discussed in other threads. I hope this helps.

Thanks @TP-Link_Deco , @deechte , @Willem_3 

I was able to upgrade successfuly... apologies on the tardy response