Hi everyone,
After multiples hours of research, I could identify the cause of the issue. I suspect a bug with the version 5.3.0.1 of the AUSST.
After watching carfully the incremental downloading of the updates on our internal update server, I've noticed that some folders storing updates were automatically deleted near the end of the synchonizing process, and this removal is not visible in the AdobeUpdateServerSetupTool.log file. Folders that were deleted include the folder who is storing Adobe Photoshop updates (named "PHSP"), reason why clients couldn't dowload their updates from this folder as it wasn't existing anymore.
We use the incremental parameter "--cleanup" to remove obsolete updates to stay on the server if a newer version was downloaded:
AdobeUpdateServerSetupTool.exe --root="F:\inetpub\wwwroot\updates" --incremental --cleanup --filterProducts="AEFT,FLPR,KBRG,ILST,IDSN,AME,PHSP,PPRO"
For unknown reason this parameter removes all updates of Adobe Photoshop and delete the "PHSP" folder instead of keeping the latest up-to-date update. It seems as well to remove other folders too which can cause update issues for other products (like Adobe Animate).
WORKAROUND:
While waiting a solution, we have decided to remove the "--cleanup" parameter from the incremental sync to avoid all updates for some products to be deleted.
Hope it helps...