@wabula 

Delete all M5s from your Deco mesh, in Deco app. Add remaining X60s as Satellites. Run Deco mesh with three X60s only.

In a similar case someone found that having X-series and M5s together causes issues till M5s are removed. I myself tried in-place replacement of M5s with X50s, achieved that with way more frustrations than I expected. System became stable after I deleted all M5s and M9s I had. My Deco mesh is X50s only, now.

I also noticed Deco app becomes much more stable when Deco mesh consists of three Deco units or less. 

I would also suggest enabling Fast Roaming back as soon as you manage to stabilize your Deco mesh.

  @Alexandre. 

Suggestion is to not mix models? 

Honestly thought that was as one of pros of deco. 

This is unfortunate as I have a wired device in the loft, which is connected to my single remaining m5. 

I will attempt to the removal of the last m5 tomorrow. 

Thanks for the reply. 

  @wabula 

One more thing: if Android Deco app is not responsive, close it completely (or reboot smartphone) so that you can manage to delete M5s in Deco app. On closing (not just hiding) and opening Deco app on Android smartphone it works (as in "not fails") more often.

After starting of Deco app wait till Download/Upload numbers are updated on main screen. That would mean Deco app updated its info and ready for you.

wabula wrote

  @Alexandre. 

Suggestion is to not mix models? 

 

Honestly thought that was as one of pros of deco. 

This is unfortunate as I have a wired device in the loft, which is connected to my single remaining m5. 

 

I will attempt to the removal of the last m5 tomorrow. 

Thanks for the reply. 

 

  @wabula 

Right now, I am thinking, your objective is to stabilize Deco mesh. You have two options: remove X60s and bring it back to M5s it were, or remove M5s and make it X60s.

After you have stable Deco mesh, you could decide what to do next.

Yes, you are right, this is one of the big points TP-Link has in marketing Deco mesh, different models are supposed to work together. Yet, there seem to be issues specifically in M-series/X-series mix. 

If you manage to stabilize your Deco mesh by making it X60s only, you would be third person in last 1-2 months on that forum with the issue of compatibility between X-series and M5s.

If you have stable X60s mesh, you might need to buy additional Deco unit instead of one remaining M5. It does not have to be X60, you could go for less expensive X10 or X20. Also, X50 and X50-PoE add-on unit can do, too.

Mixing different Deco models from same series, such as X-series, seem to be OK.

  @Alexandre. 

I may look into a cheap x substitute for m5 if it does resolve the issue. 

Small update, noticed Main deco just had solid Red LED. 

 May not have noticed before as was pure chance I was next to it. 

Seems to have resolved the issue after 30 seconds as now green again. 

  @wabula 

Do not ignore that Red LED - this may be the cause or contributing factor to issues you see. Just in case, replace Ethernet cable that connects Main Deco to ISP modem/router, or at least unplug it from both ends and plug back.

Also check if you see "Abnormal WAN speed" message in Deco app - that could also point at issues with connection between Main Deco and ISP modem/router.

-------------

When I replaced my M5/M9s with X50s, I have found X50s have much stronger WiFi signal. I had four M5/M9 Deco units inside the house, after replacing them with X50s I have found just three is enough for WiFi6 coverage everywhere. You should expect to see stronger WiFi signal from X60s, too, as they should be even more capable than X50s.

So, before getting fourth Deco, I would suggest you take one of Satellite X60 to the loft where remaining M5 used to be and see if with X60 there you still have good WiFi coverage everywhere.

@Alexandre. Thanks for all the help.
After some time messing about I have decided to return the x60 bundle.

Investigating alternative devices.

Thanks again for your advice