Recently my TP-Link Archer C7 V2 randomly reset itself. There is no pattern. I also output the system log to USB stick but there is no trace of SW reset or shutdown. Don't know what happen. Is it just aging problem and it is time to toss it?
Sounds like a Cron-Job
Power supply, defective caps?
Cron-Job: I don't have cron job to reboot at those moments. If it was cron reboot I would see some trace in log.
Power supply, defective caps: possible. I also suspect the power part. But I don't have another power supply to try it.
Try running logread in a terminal session on your "desktop". That way you can see what was being logged just before it rebooted. You could conceivably run htop or top in a different session, which would "freeze" when the router rebooted and dropped the connection, giving you a snapshot from just before the event.
I've got Archer C7s that have been running pretty much continuously since the v2 devices came to market. Admittedly, we've got pretty benign temperatures, seldom going over the 80s (F, low 30s C) inside.
Are you using the OEM "wall wart" or at least one with 1 A capacity and the proper plug on it? As I recall, it is the smaller (2.1 mm) inner pin and a larger plug might be intermittent, depending on design.