Hi @inok_spb - that's correct, the proc is dropped/created each time ProGet is upgraded/installed.

Actually, in our case, broken files are stored in the ProGet storage on a disk, I checked them during the investigation. So it's not an issue that happens on the fly during the download process. And it's also not an issue that happens during package uploading, since after uploading, packages are valid and identical to the original ones on downloading and in the feed's storage. Maybe, those packages were broken in the feed's storage a relatively long time ago for some other reason (a bug in earlier versions of ProGet? a bug in our infrastructure?). And the issue starts to be observable only now because of caches or something like that... At this point, thanks to your answers, it seems that ProGet is not the one to blame. So, I ran a script yesterday that found all the broken packages in the feed, downloaded them from nuget.org, and republished them to ProGet. It was about 100 packages overall. Now I'm sure that every package in our feed is valid. I'll keep monitoring the feed, and if new broken packages arise in the feed, I'll continue the investigation and let you know if ProGet is somehow related to the issue. Thanks a lot, @atripp!