Main network stays online while guest network loses internet connection – sometimes completely, sometimes only for IPv4 sites

The router in question is a Netgear C7800. Most of us are on the guest network, and for a few days each month, there will be a period once each day for which the guest network stops connecting to the internet. Rebooting the router fixes this. It only seems to afflict the guest network. Devices remain connected to the guest network, but are unable to access the internet. Also, it seems only to happen once a day in the mornings.

If it helps, sometimes only IPv4 sites are blocked while IPv6 sites are able to load. I’m not sure whether this is related or a separate problem, though.

Does anyone have any suggestions what the problem could be? Rebooting the router every time seems to work but is of course not the ideal solution. Thank you for reading!