Have been running 2 x Deco E4 for 2 years now without any issues but have recently hit the following problem.  When I get to around 25 devices connected the Deco no longer issues new IP addresses automatically and the only way round it is to manually set an IP on a device that needs to connect unless I reboot the router.  This could happen to devices that have been previously connected and have gone out of range then returned hours later, or simply a device that has gone into standby. 

I have completely reset both Decos and started from scratch but still have the same issue.  I am running the Decos in router mode with a Virgin Media Hub supplying the Internet feed then a mixture of wired and wireless devices running from the Deco units.

I have read about switching the DNS to 8.8.8.8 and 8.8.4.4 which seemed to be a temporary fix but only lasted for a little while.  Any other suggestions?