Unlikely, unless there is a setting in your router that doesn’t allow communication between the two bands. But then you’d lose one of them, not both. This seems much more like a duplicate IP address issue. Try unplugging all Sonos devices from power, then reboot your router. Give the router a couple of minutes to reload, then plug back in your Sonos devices.

If this indeed ‘fixes’ your issue, I’d recommend looking at the router’s manual on how to set up reserved IP addresses for your Sonos. Any router that has gotten into this state once could easily do it again. 

Your router is likely too stupid to handle multiple frequencies correctly. Try disabling 5GHz on your router, temporarily, and see if that fixes it. If it does, upgrade your router.