I ran into this at a client where we created a database in the DR site for running test cmdlets with SCOM. There are two copies of the database in the DR site. Other databases have two copies in the main site and one copy in the DR site.
You can override the default behaviour with the switch OverrideMinimumTwoCopies.
StartDagServerMaintenance.ps1 -Server DAGnode1 -OverrideMinimumTwoCopies