I'm certain I've posted this in the past, but I can't remember where.
In any of the AutoCAD versions, toolsets, or whatever they are called today.... Vault Add in functionality from the start screen is either limited or non-existent unless a drawing is already open on the screen. Some of these Add In fuctions are needed to OPEN a file. So it makes no sense to me to have to always open a file, or start a new drawing,... before I can access the Vault Add In tools.
Reference this thread and the screencast in it: https://forums.autodesk.com/t5/vault-forum/autocad-vault-add-in-team-please-explain-this/m-p/9214024...