EMC VNX5200 storage snapshot seems stuck

To perform backups, we use Veeam to utilise the VNX Snapshot feature to create storage snapshots on the EMC VNX5200.

I have a situation where Veeam has created a 'Snapshot Mount Point' and a snapshot has been attached to it, and seems stuck. No operations are able to be performed on the snapshot (detach, delete, etc) because it claims an 'attach' operation is in progress. The problem is the storage is almost at capacity and this snapshot is growing in size so I need to delete it.

When I try to detach or delete it (via the GUI or via CLI) I receive the following error:

The operation failed because the snapshot is still in the process of being attached. Wait for the current operation to finish and retry the command (0x716d80a6)

Looking at the 'Snapshot Mount Point' it is reporting as 'Offline' and if I look at the properties of the mount point I can see 'Operation in Progress' has the status of 'Attaching (100% complete)' but with an Operation State of 'Failed'.

Is there anything else I can do to resolve this situation and remove the snapshot? I've tried rebooting the SPs, but this didn't help.