This issue is most likely the result of a timing issue:
1) The package is updated
2) The PS gets a snapshot to that update.
3) Other package servers get the snapshot from the first package server. In the mean time the package has been updated again.
4) The original PS thinks it’s up to date and continues to pass out the incorrect snapshot, etc.
Package Servers which did not get the update source file had codebases of each other, the PS which did update had only the NS for a codebase. For some reason the PSs which had trouble did not update the NS to say the package was not "ready". So, the bad PSs kept asking another bad PS for the updated files.
You can prevent this issue by changing the NSConfigurator setting PkgSvrDownloadFromNSOnly=1. This will force package servers to only get its codebase and source files from the NS and not other PSs.
NS 6.0 SP3