If your MX is using site-to-site VPN, check that it is configured for Automatic NAT traversal. If it is set to manual, you may need to change the config, to reflect the new IP. Chances are it will be automatic - that's the default and most people leave it that way
Welcome to the Meraki Community! To start contributing, simply sign in with your Cisco account. If you don't yet have a Cisco account, you can sign up.