LB1120 internet stops working every few hours

Recently, the internet connection on my LB1120 has stopped working every few hours. When I log into the LB1120 modem, it shows that the internet is still connected on the modem, but no internet connectivity is reaching my router. My router _thinks_ it's connected to the internet, but no device on the network can access the internet. If I plug my computer directly into the modem, the internet connection still does not work until the modem is rebooted.

At no point does the modem say that the internet is disconnected or indicate any errors! The only thing that resolves the issue is to reboot the LB1120 modem when the internet connectivity ceases. I have tried changing from bridge mode to router mode, reset to factory defaults, turned off/on the "keep alive" setting. It is rather annoying to reboot the modem every few hours. Nothing has changed on my home network and the modem was working perfectly for the 4-5 months before this! At first, I thought the issue might be my router, but a router reboot does not fix this. Only the LB1120 modem reboot temporarily resolves the issue.