I had this problem with one of the early 3.6 betas and it would occur very frequently (every 1-2 charts). The updates seemed to resolve it, but it recently cropped up a couple of times last week. I did not taken the time to trouble shoot it. Some of my versions in the rooms go back to 3.6.15 up to the latest 3.6.19 and there may be some kind of mis-match.
All you have to do is close the print box, then re-request to print from the AC desktop and all the visits are there again. Annoying but not a major issue
