The M4 is a good system. All I could suggest is trying to set it up again in this sequence - but if you did it this way it wont help and should be stable.
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Set up your own first Deco to have the WAN port set to be in Automatic IP i.e. DHCP (& Nat) mode, it may be set that way anyway. Then, disconnect all cables from all the Decos and switch them off and unplug them. Then, put the VM Hub into modem mode
(
https://www.virginmedia.com/help/virgin-media-hub-modem-mode )
as its in MM already - just reboot it and wait for the base light to turn magenta/purple (on a Hub3 - but not on a Hub4!). Leave it 5' to initialise
Then the VM hub “MUST” then be powered off. Switch your first Deco on and make sure it’s fully initialised (leave 5 min) and then put in the ethernet cable from its WAN port to the VM hub (any port will do).
NOW… power up the VM hub and wait 5-10 minutes for The Hub to initialise and and you should get a connection. Then u se the recommended App to connect any other Mesh units to the first one. This order only needs to be done the first time you connect the router to the VM hub.
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.