@Olof I am also seeing my 3rd on the chain M5 connecting to the furthest away main deco instead of the nearby 2nd on the chain. Any update on a option to select the signal source?

Looking at the various threads on this issue it seems fairly obvious there is a real problem and should be addressed as quickly as possible. Can TP-Link confirm that this is being actively worked on? 

I got a solution now!! 
 

I got two options:

1:

On Friday I will throw the TP-link Deco M5 in the bin and never again be close a TP-Link product. Will buy the new Google Nest solution. 
 

2:

If I decide to sell my Deco M5 gear on E-bay for 1$ with an honest instruction of how it really works, I will update you guys with the link. (I trust it will go viral, if not let's crowed found some ad money for it)
 

That's probably the best we can get out of our Deco products, a laugh.. 

And TP-Link support, don't say I didn't try.. 

I have the same issue as well... all my setup can only work in a chain mode, otherwise my 3rd Deco is too far to get a good signal from the main. 

This doesnt make sense, it defeats the purpose of a Mesh system. Any if you guys has a good experience with another brand? Some of us will probably change.

TP Link needs to snswer this. Tell us it doesnt work, tell us that you have no plans to fix it, tell us that M5 is not a product you support anymore. Anything. But just answer...

Apparently they are using ping to decide path and ignore signal level, this is so wrong as direct connect to main unit will always better in ping respond, but it doesn't mean it's the best path since it might be too far to connect for 3rd unit. Who ever made the decision to use ping as the only path selection should resign and never design any network devices anymore. 

I have smart devices which are not connecting to the closest router. Resulting in smart devices with flaky connections ie not working. 

Tplink - smart devices are usually stationary , what I need is ability to assign certain devices to the router of my choosing. 

@Bobrovsky 

I think that your network is working in a "star mode". All the other members wish that the satellites can connect in a "chain link mode". If all of the satellites are connecting only to main router, is star mode. If satellite no. 3 gets the signal from satellite no. 2, and no. 4 gets it from no 3, then you will have chain link network.

Anyway i have the same issue. My location is somehow in a straight line. I've put the main router in the middle of the "line", then added one by one the satellites. 6 satellites, 3 on the left side of the main router, 3 on the right side. No matter the distance between them, they either get the signal from the main router, or they get disconnected from the network. All 7 devices are M4. The main router is updated with the latest firmware version. The other 6 have the firmware version that came "from the box". In order to upgrade them as well, i need to do a factory reset for every one of them, configure them one by one as main router and do the upgrade :)). In 2020, tp-link is selling mesh solutions that work well if you buy a 2 pack. If you want to use more then 1 satellite, they should mention that is possible only if you need a star network. Also... in 2020, if i buy a 32 devices mesh network, in order to update them, i can't do it in a decent way like other competitors by standing on my couch, pushing buttons... no! i need to use 5-10 minutes for every satellite... remove it from network, set it as main router... upgrade it, set it again as satellite. If next month we get another update... same process :)). I think tp-link should charge extra for those updates procedure, because you are also working out. You can walk, run, jump in order to reach every satellite. In 2020 tp-link is a fltness instructor.