I also have the same issue. Stopped working after the update to v6. 

I can temporarily log in by clearing the data in the device and then logging in using plarium id (will require downloading a lot of data). But once I close the game and try to open it again, same error message shows up. 

I am also using Bluestacks 5, recently updated to Bluestacks 5.9.100

I've uninstalled BlueStacks 5, reinstalled Bluestacks 4, same issue. Uninstalled Bluestacks 4, installed latest version of Bluestacks 5 and it still does the same. I can access my game on Plarium Play, but it would seem like Plarium made the new update incompatible for Bluestacks somehow. 

I am using Nox player now instead of bluestacks. It works fine in it.