Urgent Problem: Cannot open requests - View is blank

We have suddenly developed a random glitch which we cannot debug - randomly a technician will try and open a request and it will just show us a blank screen but if we go back to the request list view we can see all of them and the hover to display the description works fine as well - but select that request and you get a blank screen. If we select the template dropdown and select a template, we can open the ticket in edit mode but when we then try and view it - it is blank again.

Also, all of the reports will work fine but if we try and batch assign requests to a technician it will fail. Restarting the service seems to be the only way to get working again. Our developers are at a loss as there doesn't seem to be any pattern we can discern.

Has anyone else experienced this - and what can we do to eliminate the problem?