When your public folder content migration to Exchange Online is complete or you create public folders for the very first time, you do not have to worry about managing many aspects of public folders. ...
Updated Jan 11, 2021
Version 2.0
Blog Post
8 MIN READ
How Exchange Online automatically cares for your public folder mailboxes (via AutoSplit)
Hazem_Embaby
Microsoft
Microsofttonire Let's agree 1st that you have a huge Public Folder environment 320K here, so for the affected public folder mailbox, did you manage to see how many folders is that public folder missing ? ,cause if the out of sync hierarchy is huge that might take a lot of time and even if you did invoke the sync that is going to be splitted in to several iterations of 500 each taken in to consideration that throttling will apply to maintain a fair usage of our servers.
In addition to that AutoSplit would slowly move out folders, even if the sync didn't complete.
It would choose only 20 folders at a time, and sync those folders, and move those folders, that occurs when MRF value incremented to a certain number.
So you might keep monitoring that affected mailbox for hierarchy changes and wait for Autosplit status to change.