Public Folder Dumpster Not Purging

I am running an Exchange 2013 CU23 in a Hybrid configuration with Office 365 Exchange Online. Recently we migrated all of our user data that was stored in Public Folders in on-Prem Exchange 2013 to Office 365 and I am now in the process of cleaning up and decommissioning Public Foldrs in the on-Prem environment. The primary Public Folder mailbox (PFMailbox) was very large (685.27GB) and though all of the Public Folders have been removed, the Public Folder data stil resides in the Public Folder dumpster.

Our retention period is set to 7 days and it has been a month since the Public Folders were removed, so I would have expected that data to have cleared by now. I have researched various ways of dealing with the issue but cannot find anything that provides a clean way to force deletion of the data currently in the Public Folder dumpster.

Any assistance you can provide in resolving this issue would be greatly appreciated.