@Kevin_Z 

my modem is conntect to a switch that also acts as a DHCP server.

I have 3 z60 Deco devices. One at the ground Floor, the 1st Floor and the second floor.

the one at the ground Floor is the main deco. The deco on the ground and 2de Floor are wired and directly Connected to the router. The one on the First Floor is meashing.

the solution is in access point mode.

At leest the deco on the ground Floor and 1st Floor are flashing red heen I Loose connection. I expect also the one at the second Floor does the same.

this might sound strange bit I have the feeling the problemen start when I Connect my company laptop to the WiFi netwerk (ms surface laptop)

@Heino76 I tried everything including a factory reset of all the decos but the issue remains. 
 

the router it's connected to is even a TP-Link one 

@Kevin_Z any update or suggestions?

@Heino76 

I seem to have a similar issue.

My set-up in the UK.

Sky fibre broadband vdsl

TP Link Archer VR2100

X60 running in access point mode.

Good wi-fi signal between all X60 devices when running.

I've had the X60's now for about a week. First few days they appeared to run OK but then started to run into issues. At this point I had the mesh set-up in router mode so decided to move to access point mode if nothing else to remove any potential issues with double NAT.

Now you only have to make a change somewhere on the network and the X60's start to crash. They will be fine, then all lose connectivity from each other with the LED going red. They come back up and connect once more and are fine, then five minutes later they crash once more. The only way to get them out of this crashing loop is to power them all off completely and power them back on one at a time.

Last change I tried to make was to set up QoS on the router as i was finding downloading a game on my sons x-box or PC would take the full internet bandwidth and no other devices could get a share. Applied the QoS rule one minute later the Mesh was up and down again once more until powering the mesh once more.

At the same time I have connectivity to the router and that is running without any issue and sustaining a good internet connection.

Tired all of the documented steps such as reboots, through to swaping the main deco unit with one of the slaves with no joy. I am about at my wits end and about to go back and ask for a refund.

...

@Steve_P 

I thought it had something to do with the fast roaming option so I switched it off. It went fine for a couple of days but unfortunately I had the issue again this morning. 
 

funny thing is that it always happens with one device (ms surface laptop)

@Heino76 

i've have the same problem! Today all day no problem but we go to the first floor and the lost internet connection for 5 minutes?! I've a couple of days left to give the set back.  
is there any solution ?

@Sjek 

I've not seen one online and spent a fair bit of time looking through the forums both x60 related and others in case there was any potential hints at what the root cause might be.

Even spent some time with TP-Link support team on a chat but to no avail. 
 

They had me put the X60 main deco back to router mode with no reason why other than just trying to rule out where the issue might lay. That just causes the mesh to collapse again for a period of time. 
 

Still got the odd drop out from the slave decos tonight. So will see how it behaves tomorrow before I decide to put it back in its box and send it back for a refund.

To date I've done all of the recommended problem solving tips and factory reset and rebuilt the network twice. Firmware is fully up to date on both the mesh and the router but nothing resolved the instability. 

@Steve_P 

you hardly have any options to set so I can't imagine it's setup related. Must be a conflict between the x60 and a device or something. 

@Heino76 

He is more stable now.... i've the Sonos boost disconnected en the Synogoly Nas also. Maybe it is going to be better now?