I've double-checked the rules, but can't seem to get rid of the warnings in the Meraki dashboard.
* This shows up at the top of my screen when I log in: "As part of ongoing efforts to improve the performance and resiliency of the Meraki Cloud we will be changing the IP addresses used by Cisco Meraki devices to contact the Meraki Cloud. One or more of your Meraki devices are unable to communicate with this new IP range. For more information about this upcoming change and how to resolve the connectivity issue, please click here."
* Also, when I look at the Appliance status, there's a warning that says: "Unable to fetch configuration
This device is unable to fetch its configuration from the Meraki cloud. Please contact Meraki Support."
I've asked Meraki support and they said the ISP is probably blocking ports. When I asked the ISP, they said they aren't blocking any.
I had the same issue, with the exception of im behind a Merak MX 100! i asked support to identify what device was complaining, it was one random switch while the rest of my environment was fine. i went and rebooted it and the dashboard notice went away about a day later.
Support also gave me the same response but, like you i know our ISP isn't blocking anything. I suspect its a bit of a bug in the MS software.