Cant delete a project from Trash

[ChrisM]

I have migrated a classic project into out cloud Jira, Now I want to delete the project so I can repeat the migration. I delete the project and it goes to Trash. I try to remove it permanently and I get a message something went wrong - try again. Tried many times with the same result.

[Karl Hubner]

I ran into this very same behavior, just yesterday.

Due to some urgency, I resorted to opening a Trouble Ticket. 

From the comments I received via Tech. Support, it turns out that one Issue in the Project (that would not Delete) "had a huge history". 
They apparently had to Restore the Project, and Delete Issues from it... until they could successfully Delete the Project, themselves.

Now I can continue with our Migration!