The recent server updates on the 8-10th February introduced an intermittent attachment issue that was uresolved with the roll-outs of the following week.
The issue has been widely reported on all Viewers, and in some cases wrongly labelled as a Phoenix Viewer issue (I’ve recently assisted people using Phoenix, 1.23.5 and Viewer 2.4).
A JIRA has been raised on the issue, and the Phoenix team have posted some useful guidelines on dealing with matters (with thanks to CS for bringing this to my attention).