Unfortunately, there is currently no known workaround for a user to resolve this issue. We are still tracking down the underlying cause (whether internal or external), but from what we can tell the error is only resolvable with a manual fix on the backend; in essence, there is a lock on the virtual container that is very rarely not getting removed when the sandbox restarts, and if it is not removed by the normal sandbox shutdown procedure, it must be manually overridden.
As you said, it is tied to the campaign, so you could ostensibly create a copy of the game and everything should then work as normal in that campaign (as it would create a new sandbox), though naturally that comes with the occasional hiccups of using a copied game.