Hi Todd,
My understanding is that Meraki is providing NetFlow data in a non-standard format that many monitoring tools have trouble with, due to the Meraki-specific implementation of NetFlow.
There is a little more information to be had regarding the situation - as covered here: https://www.plixer.com/blog/netflow-reporting-2/meraki-netflow-support/ :
"NOTE: The Meraki documentation states that “The MX and Z1 do not support exporting an SNMP ingress or egress interface index via NetFlow.” This means that some NetFlow Analyzers will not be able to report on the export."
This is (unfortunately) not the first time we've run into this issue, and the most effective thing we can do at this point is to encourage Meraki to fix their NetFlow implementation - by having customers provide them with direct feedback - which can be done through the Meraki interface: https://meraki.cisco.com/blog/2014/07/make-a-wish-2-0/
Best,
Kerry