We successfully upgraded to SLM 9.x, so thank you to all who posted suggestions and prerequisites.
A couple things I notice post upgrade.
Everything that was in Quarantine went back to Active. Not a big deal, but not sure why. I checked the Quarantine settings in the SMACC and they are all correct. And there are errors in the DUJ related to Quarantined items. I have a ticket open with SNOW Support for that.
I also notice in the report, "computers that are not inventoried", a new source of "Virtual Management Options", shows up, along with a lot of client/quest VM types. Also, I notice the "Network Discovery" source type is not there, but AD Discovery is still.
This begs the question, does something need to happen on the Inventory Server Gateways along with the SLM upgrade? Is that where Network Discovery is coming from?