Staged 3rd party artifacts have been dropped without telling me why

After successfully uploading a 3rd party artifact bundle (the Rats! parser generator and runtime), I get an email that tells me that staging is completed.

Nexus itself tells me:

Artifact Bundle upload finished successfully
The following staging repository has been created ...

But after an hour or so I got another email that told me that the staging repository was dropped but the email doesn't give a reason.

I've uploaded the bundle again:
https://oss.sonatype.org/content/repositories/central_bundles-345

Please let me know if the bundle is missing something.

Thank you!