Yeah, I use Meraki for my home and the only thing on the outside of my MX is a Comcast cable router. I'm kind of confused why it would say one or more of my devices won't be able to communicate to the new IP range. I'm assuming it's just an erroneous notification at this point.
We’re aware that email notifications were sent to some network or organization administrators where no firewall issue exists, and we’re working to improve our testing to avoid these false positives before any further notifications are sent. However, most notifications were sent correctly: if you did receive an email notification for a network, please double-check that any firewall rules are configured properly.
Meraki Backend Infrastructure