If an event UID property contains special characters, e.g. @ it is not possible to update/delete such an event in the Calendar UI.

<multistatus xmlns="DAV:">
  <response>
    <href>/cal/admin%40domain.tld/5d2cbdd3765b-7b95e9973638-1887c2be/5u3k19j0v4rd6uinh7uiq%2540google.com.ics</href>
    <status>HTTP/1.1 404 Not Found</status>
  </response>
</multistatus>

You can see the initial %40 (@) is double-encoded into %2540, which is the problem.

Server DAV: Radical.