I have the same problem. They all go off line after a few days or weeks. Only power cycling will bring them back. I travel in Europe often and have no way of cycling power from there. It makes the cameras useless to me. I think I will install a timer on the AC power to cycle power once a day to keep them going.
Another option for you is to use a smart plug to power cycle the cameras remotely. I have smart plugs installed for each of my cameras and it makes power cycling easy and simple using the app.