Cannot set up whitelist.  Check log of Antivirus. Is there anything related to youtube?

May disable antivirus to see what happens. Contact tplink if problem not solved.

@Pinstripe , hi !

I have a similar network setup and the very same issue you have: youtube app or in browser do not work in my network using several different devices like Smart TV, PS4, Roku Express, iPhone, iPad, although youtube works on macOS devices... interesting enough, it worked fine until a few weeks ago and I can't recall any event that determined the issue to arise.

I already tried to disable the antivirus and even reset the whole configuration but still no success with youtube - all other streaming services (Netflix, Disney+, etc.) work fine.

As I was unsure if the problem is with Deco or my ISP, I replaced the main router by an Apple's Airport TimeCapsule - and youtube worked everywhere!  So, definetely, Decos are causing the issue !

My Decos firmware are 1.2.11 Build 20190926 Rel. 55727 and there is no new update.

I am very disappointed!

Did you have success finding a solution to your issue?

@Akhenaton Hi there,

I concluded that the source of my problem was I bought my Deco Mesh from a German supplier, and its Homecare antivirus was getting updates from a German/EU server. 
Because I live in the UK, all my Netflix/YouTube/Disney+ was being blocked because they're hosted on a UK server - i.e. they were being blacklisted on the German antivirus "safe list".

To test this; I set the Decos to AP mode and had them link up to a UK-supplied Archer C4000 router that comes with the same Homecare antivirus. I have had no issues with anything being blocked since using this setup, and I think this is because the UK antivirus is recognizing UK apps.

I could be completely wrong and it could be a huge coincidence, but it's been working fine ever since.

It's a bit annoying that it took an extra piece of equipment to get it all to work.  I bought my Decos from Germany because I live in an old tenement flat with thick walls. At the time of purchase, UK suppliers were only providing Decos that came in 2 packs. Based on TP Link's specifications, I realized a 2 pack wouldn't cut it in my building, I needed a 3 pack to ensure complete coverage. Buying a 3 pack from an international seller was cheaper than buying a 2 pack and a single pack here - but it wasn't without its pitfalls! :)

So I would recommend you try getting your hands on another TP-Link router with Homecare built-in and test that. If you stop having issues, you can set Deco to AP Mode and run everything through the other router. If you're still having issues - perhaps it's worth contacting your ISP.

Good luck!

@TP-Link Hi,

Doesn't M9plus automatically update itself?

I have another TP-LINK router that is bricked due to a firmware update...

Claudio.

@Akhenaton If you have the Deco app - you should be able to push the update onto it that way. 
 

If that doesn't work - then the above manual update links should.