It looks like it was a temporary issue. The "Run in Sandbox" button is enabled again over here.
Are all Sandbox problems resolved? I still have problems deploying a project to the cloud for the first time (5.13.0).
When deploying to the cloud i get the error: 'Whoops something went wrong while deploying to the Sandbox.' When I then press 'View app' my browser shows a Mendix error: 'internal server error. An unexpected exception occurred while handling request login'.
If i remove the extra login credentials from the URL i do get a login screen. But since I do not have any users yet I can not log in.
Another Sandbox project i have seems to be deploying/running again as it used to.