@darkyto The issue is now even worse.. The secondary decos are loosing connection and dropping on a regular basis.

Here are some of the logs that I've extracted:

Wed Dec  9 11:59:14 2020 user.warn IMPROXY: WARNING[mcast_recv_igmp@753]: Don't exist this Downstream VIF
Wed Dec  9 11:59:26 2020 user.notice dhcpv6: teardown, interface=wanv6 ifname=br-wan
Wed Dec  9 11:59:26 2020 daemon.notice netifd: wanv6 (16632): RTNETLINK answers: No such process
Wed Dec  9 11:59:26 2020 user.notice dhcpv6: teardown, ip -6 route del ::/0 dev br-wan
Wed Dec  9 11:59:27 2020 daemon.notice netifd: Interface 'wanv6' is now down
Wed Dec  9 11:59:27 2020 daemon.notice netifd: Interface 'wanv6' is setting up now
Wed Dec  9 11:59:27 2020 user.notice dhcpv6: start dial, iface=br-wan
Wed Dec  9 11:59:41 2020 user.notice dhcpv6: teardown, interface=wanv6 ifname=br-wan
Wed Dec  9 11:59:41 2020 daemon.notice netifd: wanv6 (16924): RTNETLINK answers: No such process
Wed Dec  9 11:59:41 2020 user.notice dhcpv6: teardown, ip -6 route del ::/0 dev br-wan
Wed Dec  9 11:59:42 2020 daemon.notice netifd: Interface 'wanv6' is now down
Wed Dec  9 11:59:42 2020 daemon.notice netifd: Interface 'wanv6' is setting up now
Wed Dec  9 11:59:42 2020 user.notice dhcpv6: start dial, iface=br-wan
Wed Dec  9 11:59:48 2020 user.warn IMPROXY: WARNING[imp_verify_multicast_addr@206]: Group address ff02::fb is link-local multicast address
Wed Dec  9 11:59:48 2020 user.warn IMPROXY: WARNING[imp_verify_multicast_addr@206]: Group address ff02::fb is link-local multicast address
Wed Dec  9 11:59:48 2020 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.252 is Local Network Control Block
Wed Dec  9 11:59:49 2020 daemon.err udhcpd[5947]: Sending ACK to 192.168.68.111
Wed Dec  9 11:59:49 2020 daemon.err udhcpd[5947]: clear ip c0a8446f
Wed Dec  9 11:59:51 2020 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.251 is Local Network Control Block
Wed Dec  9 11:59:52 2020 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.251 is Local Network Control Block
Wed Dec  9 11:59:56 2020 user.notice dhcpv6: teardown, interface=wanv6 ifname=br-wan
Wed Dec  9 11:59:56 2020 daemon.notice netifd: wanv6 (17269): RTNETLINK answers: No such process
Wed Dec  9 11:59:56 2020 user.notice dhcpv6: teardown, ip -6 route del ::/0 dev br-wan
Wed Dec  9 11:59:57 2020 daemon.notice netifd: Interface 'wanv6' is now down
Wed Dec  9 11:59:57 2020 daemon.notice netifd: Interface 'wanv6' is setting up now
Wed Dec  9 11:59:57 2020 user.notice dhcpv6: start dial, iface=br-wan

I have used QoS to set my Desktop as the only priority device - I have also used my IPS bandwidth speeds. Still, I am noticing that from time to time the connection simply drops even when all other devices are turned off (no smartphones, no Alexa, no laptop, no PS4, nothing active apart from the Decos and the desktop PC).

I've also noticed that if I turn on WiFi on some smartphones then the Decos are immediately disconnected - for example, this happens when my wife uses WiFi on her Samsung A3. Turning of the WiFi on the smartphones improves the situation a bit but still.. this is a no go and the Decos are still dropping.

Anyone from the support here? I am accepting any ideas on how to improve the situation  - the Deco mesh system was bought just a month ago and used to work perfectly until recently.

I had to send the whole 3-pack system to the authorized dealer for repair. However, I am doubting that the whole product is faulty as I am seeing multiple reports that Deco M4 and M5 are not working properly. They are pretty unstable with disconnection issues all the time and the speed is lowered on the secondary Decos.

Now I had to revert to an old 2.4Ghz router and use a 3rd party extender - as a result, my speed is again what it used to be which translates to 10x faster than what Deco M4 was providing. Not to mention that I am no longer having troubles with connecting Android devices and the connection is stable.

As conclusion: the Deco M4 was a disappointing purchase which became a burden in less than a month.

Just wanted to confirm your suspicion I initially bought the m4r with the 2 m3w kits, the m3w’s kept disconnecting from the m4r. So I replaced the m3w with an m5. So I had the m4r and m5, everything was great for awhile. Then I updated the firmware on both and experienced the same exact issue you described with the speed dropping to 3-6mbps. Also need to mention I have an Ethernet wired back haul for the m4r satellite, the M5 is main deco. Well my devices for m4r kept dropping. So I swapped the m4 and m5 locations and the issue seems to follow the satellite. Well I didn’t have time to troubleshoot due to work so I bought another m5. Same issue. I also then bought a w2400 pair from Walmart. Same problem, even downgrading the code on the w2400 and m4r did not resolve it. There is definitely a firmware problem with the back haul. Devices connected to the main deco were fine only when connected to the satellites it becomes and issue. Definitely the problem is the back haul/front haul. Just to note by trade i am a network engineer. I have cable testers, crimped my own cables, connect the main deco direct to the satellites, set up the w2400’s as my main environment then the m5’s , then a mix of the m4r and w2000..... all the same issue. Used a 100’ cat 6 cable to connect the main and satellite and moved the deco around my second floor and nothing ever changed. For me I’m guessing firmware problem.