Just as an idea, try examining the logs of the modem/router, and if this reboot is issued by the modem/router itself, then it should have a log file of the activity.
You might also want to try using a different power outlet to eliminate any possibility that this reboot is caused by a deteriorating outlet in the apartment.
You might also want to try using a different power outlet to eliminate any possibility that this reboot is caused by a deteriorating outlet in the apartment.
