Have customer syncing his Business OneDrive on his personal laptop with Office 365 and his work desktop. The document was created on the laptop, and synced with 365. When he got to work the document wasn’t on his work machine and when he tried to sync he got the following error.

With more probing I found out the  customer had a 40 gig folder he was syncing and it just took time.  That is why the “already syncing” warning came up.

I hope this helps someone else out there…