We upgraded to a new version of Cacti (1.2.17) and could not get graphs to show for our Meraki MX devices. Everything was working fine in our older Cacti environment. (We actually did a new install to move from a no longer supported version of CentOS to a current version of Ubuntu Linux).
It turns out the "Downed Device Detection" default setting under the "Availability/Reachability Options" for the device was "SNMP Uptime". Once I changed to "Ping or SNMP Uptime" the graphs worked!