If I told you the MS-390 was running IOS-XE would you be surprised?
I was troubleshooting a DOA one and discovered the serial console port under the cover next to the mgmt ethernet.
It seems to be pretty much a modified C9300 running the Meraki stuff as a process or container under ios-xe. I had serial on it when it upgraded and it definately didn't reboot (Was using the serial to troubleshoot it not seeing compatible SFP's - it's IOS-XE denying them - also I suspect why the portal doesn't show SFP info on the MS390 and why a bunch of the various bugs exist.)