Well you aren't supposed to use test net addressing in your customer networks, so perhaps they saw it fit to use those in their internals so they would never conflict with RFC1918 addresses.
Strictly speaking, it is reserved for documentation (see the RFC).
One could argue whether Meraki is simply following the standards/RFCs or whether you should be able to use it (and violate the RFC). To be honest,I don't think the forums will help you with this issue.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
Please, if this post was useful, leave your kudos and mark it as solved.
