I'm using one of older routers as a WiFi extender. It's been restarting often, I thought it was broken. After spending some time investigating I had to laugh, as I figured out *I* was the cause...
I set up the router to restart at 4:00 AM due to previous issues (https://xkcd.com/1495/). Later I changed the internal network IP on the "main" router without changing the static IP on the "extender". The "extender" was still able to act as AP/switch so I did not bother to reconfigure it, but it could no longer "connect to the internet" itself.
This turns out to be a problem, since whenever it's rebooted, it relies on NTP to get the current time/date. With no way to reach internet, it was always start at Jan 1st, 00:00:00 and never update the time. Then, 4 hours later, the configured reboot time would kick in, the router would reboot, usually during the most interesting point in a movie. And of course, the timer would start ticking at 00:00:00 again...
