Alert Policy can't be deleted nor deactivated

I have added a Policy under Alerts to monitor Free Disk Space. Now I'm getting the following error Message everytime I click on Alerts: Something went wrong. Please try again or refresh the page.

I tried to remove this policy but I still getting the same Message. Editing or deactiving also the same Error.
I tried using 3 different Browers and from 2 different Networks.

I still can create a new Policy and edit it or delete it as I want. Yet I will see now Alerts because of this "Free Disk Space" Policy.
I removed the Managed Device hoping that the Policy can be now deleted, but that didn't help. In fact the Policy still has 1 Device under Devices monitored, although my Dashboard is now empty and no devices at all to manage.

Any Idea how to solve this issue? I can live with a bugged Policy but like I said it prevents me from seeing any Alerts from the other policies