We have the same issue running 2.1.0p5.
We are loading all resource groups based on a tag, some virtual machines are returned but others aren’t. The only thing I can see from the returned check_mk output is that the resource group may appear in lowercase and uppercase.
I have also noticed that using 2.1.0p20, the billing information isn’t returned, the agent gives an error on the output. “agent-bailout|[2, “Usage client: //?”]”, works fine in 2.1.0p5.