I just wanted to update you hopefully for the last time! The issue I was having was an electrical issue just like you thought.
While I was in the US, my wife was telling me the problem was getting worse, then the modem, and Apple TV started randomly rebooting as well. Our landlord sent us notification that electricians would be working on our building yesterday. Since the power came back on everything has been fine.
I kept the cable box on all afternoon yesterday, and again this morning. There has not been ONE reboot!
Thank you for your help.