There are several discussions explaining how VRRP works. See one of them.
https://community.meraki.com/t5/Security-SD-WAN/Does-Meraki-MX-Supported-LAN-VRRP/m-p/50047
"MX uses the VRRP, for sharing uplink health and connectivity status information between appliances.
VRRP heartbeats are sent across the LAN interfaces on each VLAN every second.
If no VRRP keepalives are heard by the secondary MX on any VLAN after three seconds, the dead timer will expire triggering a failover event."
The concept is explained neatly at the following Urls.
https://documentation.meraki.com/MX/Networks_and_Routing/NAT_HA_Failover_Behavior
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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