C6300 Periodic Disconnects

I have a C6300 cable modem/router in a vacation home, with only 2 Honeywell wifi thermostats and a Chamberlain wifi garage door opener connected via wifi when the home is not occupied. Since it was installed, the router would occasionally stop working and require a manual reboot to reestablish connection with the wifi devices. Thinking that the problem was due to occasional power outages in the area, I installed a modem/router UPS, but the problem persisted. I then installed a timer between the UPS and the router that shuts off power to the router each night and powers it on again 2 minutes later. The modem/router reboots automatically each night, and this seems to show that power outages were not the problem. I still get periodic messages from Honeywell that my thermostats are not communicating with the router, although they do reestablish the connection after the nightly power off/on cycle. The thermostats do still operate the heating system when they are not online. There are not any other wireless or wifi devices in the house that would interfere with the wifi signal. Can anyone suggest why my modem/router would randomly disconnect from the Internet and not function again until being powered off and on? Thanks in advance for your help!