I have had an AC2 router for 6 months and I have the same issues at least once a week.
All of my devices can find the router, however, there is no access to the internet. The devices usually drop out one by one.
The cure, is to turn off and turn on the router - Yes, its a solution, but I would rather that it just works!
Could it be that the router is limited by the number of ip addresses?
Any advice or help - very gratefully received.