VS PMC EF commands error: Unrecognized command or argument 'C#'

In Visual Studio's Package Manager Console (V 6.6.0.61), the commandget-migrations, and other Entity Framework commands, output:

Specify --help for a list of available options and commands.Unrecognized command or argument 'C#'

I have successfully run this and other EF commands through the PMC within the last week. But, seemingly all of a sudden, these commands produce the above two-line output. I have installed EF V6.4.4, verified by Get-Package and Get-Help about_EntityFramework.

I am using ASP.NET MVC 5, not Core.

get-migrations in PMC usually lists the migration files that have been implemented since the seed method. I'm particularly confused because "C#" doesn't appear in the command itself...

It looks like someone posted just this question a few days ago, but the author removed it.

Any ideas as to what might be causing this?