I have noticed that when I have a text box that has words and a picture in line with the text express sometimes generates an image that is 194x194 pixels of the top left corner of the picture rather than an image of the whole of the text box. If I "fiddled" with it a bit I could trick into working properly.
It just happened again in a new document so I created a test docx with one of those situations and duplicated it. I found that all I had to was to grab the bottom handle on the text box and make the height of the box slightly smaller. The documents attached - the first fails and the second one works.
Any ideas what is going on and how can I know in advance which ones will give a problem