Hi Ernest,
Thank you kindly for the support response. You were correct in that it was these exclusions that were the culprit. Everything was working as it should be. It’s just that the client inadvertantly tagged posts with these excluded tags without being aware. They were set up a number of years ago and I had not had to do anything in Ajax Search pro since then so I got completely lost looking for a bug and not spotting the obvious which you kindly pointed out.
Many thanks for your help,
David