Hello, I've also been experiencing this for a few months now - just been too lazy to try to get it sorted!
Definitely not WiFi as happens across all devices simultaneously, including a wired tower pc.
Usually I'm able to gain access to the router's configuration via browser, which seems to say connected (& ping / traceroute works! on off on off every 30 seconds or so) but pages won't load, and each device shows up 'no internet' or similar on settings. Restarting the router generally fixes it for a while, but yesterday the router's config was unreachable and a reset was required, which fixed it great but back to intermittent again now.