My problem could be solved today by the TP-link  support with a friendly remote support.
I understood that it occurred because I had 2 Archer C6s running in access point mode and one was working in the 20MHZ and one in the 40 MHz range via the Auto Mode. With firmware version 1.3.6 on both devices with fixed to 20MHZ, the 2.4 Ghz IoT smart devices no longer disconnect.

It looks like everything is working normally again.  

@Solla-topee Let me get this straight. I have two OneMesh compatible devices, but they won't work together. Only option is to buy another piece of hw. That's ridiculous. 

I appreciate your answer of course.

@Solla-topee 

This is a joke, in the "TP-Link OneMesh Devices list" it never says that you can't use two routers. I just bought two archer C6, wired my whole house so that i can have one in each end of the house. And after all of that work I find out that I cant use two routers, this is completely misleading.

I understand that there is a FAQ list somewhere, but if you have a list of compatible devices i expect them to work together, even if it is the same device, or at leat be clear on the fact that it doesnt work.

It's a shame from you tp-link

I have an Archer MR600 in the basement (much concrete), an Archer C6 and two RE300 repeaters. Please provide the option to use the C6 as AP with mesh functionallity. This is not an unlikely use case. In my case I use the MR600 and one RE300 to cover the basement, the C6 to cover one side of the first floor and the second RE300 to cover the other side (ideally connected via Onemesh to the C6).

 

Or is it possible to connect one RE300 to another via Onemesh so that I can skip the C6? In my case the positioning is topological given. The MR600 has to be in the basement and can not be positioned in the middle of the house.

São oportunistas, beira a trapaça. Também comprei um segundo Archer C6 para usar como rede mesh, acreditando não haver nada mais compatível do que dois Archer C6 trabalhando juntos.