How are the two MX's configured? I.e do they plug directly into your ISP's network with Public IP's directly on the WAN interfaces or do they have a ISP modem upstream and have private IP's?   If you're suspecting an issue with the VPN Registry communication, numerous alerts will be generated within your event log of the MX in question. If you're seeing alerts of VPN discconect a lot, this would point to this. I've had this problem in the past and had to engage Meraki support to manually change the registry that the MX was trying to communicate with to stop the problem. ... View more