I agree, this could be an environment issue, but for certain this is not a VM environment issue. The Pega app is running - otherwise you would not be able to access Dev Studio - so the bits of the VM (CentOS, Tomcat, and PostgreSQL) are functioning as expected. This VM is in wide use, and this is the only reported issue of this type.
I see you are using Safari. I am a Mac user as well, and I can access the flow diagrams just fine in Safari on macOS Mojave. It is possible your Safari Preferences are blocking the form from displaying correctly.
My recommendation is to try using a different browser.