Users.GetOrgScopedID failing (breaking our games account login!)

Hi there. As of a couple of hours ago, calls to Users.GetOrgScopedID from our Unity based titles have started failing intermittently with the following error.

"Failed: Server response is not valid JSON"

The player account management for our games relies on this call returning a value in order to authenticate the user and allow them to play our games. I'm hoping to escalate this ASAP as it is preventing some of our players from accessing our games. Any insight would be greatly appreciated. Thanks!