I thought I'd make a separate post for this, there are similar 15.21.1 posts, but not quite the same. Our issue was once we upgraded from 14.33.1 to version 15.21.1, we experienced errors about poor/no connectivity to the Meraki Cloud. Working with support, the tech noticed some network configurations not to best practices. The one causing the cloud connectivity issues was the switch management vlan was set on both the core switches and MX. Changing the gateway of the switches from the core switch gateway (example: 10.10.1.1) to the vlan gateway on the MX (example: 10.10.1.254) resolved the connectivity issues. It seems the newer 15.21.1 is less forgiving to bad configuration 🙂
