I have the same problems, ive tried all of those solutions as well. I have a replacement coming soon , but after looking at the forums, i think its a software issue vs hardware issue.

@Aaron_G @Kevin_Z 

I get feeling that TP-Link dont care about this at all... Many Many people complain about this problem.

Here on official forum people post the problem, but it takes days, weeks before members of TP-link react. 

I hope TP-Link will look into this serious otherwise i bought a product thats not good, waste of money.

I never had those problems with my Apple TimeCapsule !!!! So its not something of the devices that is connect to TP-Link otherwise i had already those problems.

TP-LINK take your responsibility and investigate this!!!

@poudenes Indeed is software related.. and i feel that they don't care too (or they aren't good enough to sort out the problem). Otherwise a fw release had came out.
I will pass through and switch to a Fritz! environment. 

Obviously I will NOT advice anyone to pass over TP-LINK mesh devices anymore

@xCape hi i had the same issues i tried many thinks all the above mentioned solutions, fixed static ip, update power on off. At the end i made deco to act like a acess point (settings)because in the settings was set up as a router and it made a conflict with my router and thats what the problem was, no desconnections now i hope that this will help you. I fix this today after a lot of effords, i will lets you know in a couple of days again.

@johncharitos 

For me my Deco must be a router. My modem (router) of Ziggo is on pass-true mode. So its doesn't do anything.

Im still have the idea that TPLINK doesn't care about this... it take years before they give a reaction.

No any other support to check things ( We all here have tried everything.... )

@Aaron_G @Kevin_Z  are you both still there?

@johncharitos 

this is a workaround not a fix. this means i should demand my old router to manage open ports, redirections... and i don't want to. This is the main reason i switched to another router (along with signal boost)

@xCape 

If you're fast maybe you can buy this:

https://www.ibood.com/electronics-nl/nl/product-specs/60783/284497/linksys-max-stream-ac-mu-mimo-triband-router.html

Linksys Max-Stream AC5400 MU-MIMO Gigabit Router 139,- euro only today

@poudenes 

Thanks for that.

I returned TPLink to Amazon and ordered a MESH system by AMV Fritz! (7590) that will replace my modem as well.

I am truly happy now. Signal strenght over 3 floors and 20mt far away home in the garden

@poudenes 

I found the best solution was to to disconnect Deco completely wasting 4 units.

I have reverted to my old AV500 extenders also made by TP Link.

Needless to say Tp-link/deco will not feature in future purchases!