Merge fields in templates not working

Merge fields in templates not working

Hi
I have a template set up. It was working absolutely fine until a few days ago. Not sure why it stopped but, here's the problem. 
The merge fields don't fully populate. If I hire through the candidate, the company name isn't picked up,  but all the other parameters are, if I hire through the job opening, the candidate name doesn't get picked up. The weird thing is that when I test it through a test candidate and job opening it works but on 'live' cases it doesn't and I don't understand. All the merged fields are copy and pasted, as advised, into the template.
Anyone have any ideas on how I can rectify this?
Thanks