Hi,
This is our setup, we force build all our products once a week and delete the nuget cache on the build server the night before. We had the default retention rule to delete packages that have not been requested in the last 90 days and that have been downloaded fewer than 1 times.
This works fine but packages that where downloaded once by a developer and later replaced by newer versions started to accumelate so I changed downloaded fewer that 1 times to 2 times. Reasening that every really used package is downloaded at least 12 times in the last 90 days because of the cleaned cache and the forced build.
Somehow this week packages that are clearly used are missing and I can see in the retention log that they have been deleted and i'm sure that they where downloaded more than twice in the last 90 days.

