Hack at the problem until its reduced to its purest form.
> My devices remain connected to the network, but all traffic dies.
Can the devices send packets within the network, but not the internet? Use ping to double check. if no, do you have any wired devices to confirm rather or not its wireless interference vs the router doing some sort of maintenance task.
Does this impact all protocols? tcp/udp/imcp. I've seen random network hiccups only impact tcp before.
ping tests imcp, dns (nslookup on windows/host on linux) tests udp (and can also test tcp) http tests udp and tcp, depending on browser and service. curl can let you confirm the test is going over tcp.
MTR is likely your final solution for investigating this. It is like a traceroute that rapid fires out to get second by second details about all the hops in a network path. The types of errors you get can also tell you why.
If it ends up being tcp only and internet based, things get harder, some mtr clients support using tcp instead of imcp to find hops where tcp breaks, but your isp routers might also refused to reply to such packets directly.
Finally, watching the lights on the router and modem (if seperate) can be illuminating. First, get a feel for normal light operation, normal activity blink speed, etc, then starting a few minutes before the event normally happens, just observe the lights for changes until the event ends while also using your phone to know when the event has started and ended.
On that note, look up how to access web consoles on the router (and modem if seperate). They may have event logs that tell you if anything is happening, like ip renewals, or if they are getting commands from the isp to do things.