Projects with negative package storage size

We are seeing a small number of projects which are reporting negative package storage size: https://app.periscopedata.com/app/gitlab:safe-dashboard/919346/Storage-Limit-Exploration?widget=15042052&udv=0. Currently it is 105 projects representing less than a GB in total. This does not seem too significant, however it could be confusing to end users and it would be good to know what is happening.