This has been an issue since 8.5 for us and happens every time:
1. We do the upgrade
2. I build new image and capture it, deploy to out
3. Imaging will be working great
4. Within 24 hrs all of the package servers will start lose the image file
Attached is image that show this, the agent on the package server shows it download the file, but if you go to the folder that file should be in its empty, this will start to move through the system until all of the files are like this and I need to capture a new image file to deploy out