Single user unable to see mailbox

[LawesD]

Hello! I have a niche issue and would appreciate any help. 

I've got a single user who suddenly is unable to see any mailbox details after clicking on the envelope button. Just a blank space within the hornbill frame. 
No change to user profile or roles, has been using for years.
No change when using different browsers/machines so I'm confident the issue is in Service Manager somewhere

His link goes to
https://live.hornbill.com/uopservicedesk/messages
Same thing happens when given the full URL
https://live.hornbill.com/uopservicedesk/messages/?mailbox=helpdesk
 

TIA

[Jim]