Now that we are fully into database upgrades, here is an important item to be aware of:
As you may know, the Database Vault (DV) option could be reported as not installed in source when converting non-CDB to PDB, and the target CDB has the option installed. However, be aware that is not supported to remove DV option in a multi-tenant environment (single-tenant included).
From Doc ID 2380950.1:
IMPORTANT: Never run dvremov.sql on a container database (CDB) / Multitenant environment. Doing so will cause serious problems when upgrading the PDBs.
In case you run dvremov.sql in a 12c multi-tenant DB, then the only option you might have is to restore the database to the state before running dvremov.sql. Assuming you have this backup, of course.
So stay sharp!