Try to access directly by the IP that the MX is configured.
https://documentation.meraki.com/General_Administration/Tools_and_Troubleshooting/Using_the_Cisco_Me...
- MX - (varies)
Most MX models have a dedicated management port used to access the local status page. In addition, the local status page is accessible at the MX's LAN IP address for all models.
By default, MX devices run DHCP. Once the client is connected to a LAN interface of the MX, find the client's IP address and default gateway, then open the default gateway address in a web browser.
Note: If the MX is in passthrough mode and its uplink is on a subnet that overlaps with a remote subnet over VPN, either the MX will need to be temporarily removed from VPN to be accessed locally or the local status page can only be accessed via VPN.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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