Changing to unique ID’s resolved the issue.
Thanks very much!
So turning off the DataTables JavaScript library in the TablePress table fixed the issue.
Thanks for your help!
For comparison, here is an example of a post where the image pop out is working:
http://lafeber.com/staging/vet/required-reading-for-veterinary-staff-zoonoses/
Here’s one of the posts where it isn’t working:
http://lafeber.com/staging/vet/body-condition-scoring-the-sea-turtle/
I’ve tried re-inserting the images both with and without the class=”fancybox image” and re-creating the post, but get the same issue each time. It’s just two posts I’m having trouble with, the rest work fine. Hope this helps.