OK I found the answer in another post. Sorry for not searching more thoroughly.
Answer here http://support.advancedcustomfields.com/forums/topic/import-twice-an-existing-fields-group/
But just in case I will provide the answer links here.
Using Local JSON you can create a folder in your theme which will save JSON files and then when you upload these they can be synced.
Its worth noting that the sync field will not appear until it finds something to sync.
http://www.advancedcustomfields.com/resources/local-json/
http://www.advancedcustomfields.com/resources/synchronized-json/
Hi
I solved the problem, the issue was that the custom fields were set to different categories. I am guessing when I imported the fields the were set with category id numbers and these changed on the new database.
All working now.
Thanks