I have about 500 contacts from three AS acccounts, almost all of them with a picture. After a while, weeks or months the contacts start loosing their picture. I checked with impostah the file entry. The files containing the image are really gone. With a simple copy I can get them back. I already increased the file-cache/contacts partition and modified the watermark file.
A simple disable, wait for a few hours till contacts are gone and enable contacts of the AS account solves the problem.