SharePoint files not syncing to File Explorer

/01 — TWO ROUTES, NOT ONE

Sync and “Add shortcut to OneDrive” are different things

Both routes use the same OneDrive app — the cloud icon by the clock — signed in with your work account, and both end with the library’s files in File Explorer. But they put them in different places, they fail differently, and Microsoft will not let you use both on the same library.

• Sync is the older route. Press the Sync button on a library in the browser and the whole library appears in File Explorer under a heading with your organisation’s name, alongside your OneDrive. It is the route most offices set up years ago.
• Add shortcut to OneDrive is the newer one, and the one Microsoft now leads with. The library appears as a folder inside your OneDrive, follows you to any PC you sign in on, and behaves better with large libraries.

The two collide. If a library is already synced, trying to add a shortcut to it fails, and the other way round; you will see a message that the folder is already being synced, or that a shortcut already exists. So when a library has vanished from File Explorer, the first question is which route it used, because that tells you where to look for it and how to put it back. A library under the company name was synced; one inside your OneDrive folder was a shortcut.

/03 — THE FILES THAT JAM IT

The handful of files that stop the whole library

One awkward file can hold up thousands of good ones. View sync problems names them; these are the reasons they are on the list.

• The path is too long. SharePoint on the web tolerates deep folder trees and long names that Windows cannot: the full local path, from the drive letter to the end of the file name, has a limit of around 260 characters. A library that is fine in the browser jams the moment it is synced to C:\Users\YourName\Company Name\.... Shortening a folder name or two near the top usually clears a whole run of errors.
• Characters Windows will not accept. Names containing " * : < > ? / \ |, or ending in a full stop or a space, cannot exist as Windows files. Rename them in the browser.
• A file that is open. A spreadsheet someone has had open for a week, or a file another program has locked, cannot be updated until it is closed.
• Too many items. Microsoft’s own guidance is to keep the total across everything you sync under about 300,000 files; beyond that the app slows to a crawl and looks stuck. A whole-company library synced in full on every laptop gets there sooner than you would think. The remedy is not to sync the whole library: use Add shortcut to OneDrive for the folders each person actually works in, or choose folders in the app’s settings.

/05 — WHEN IT IS NOT YOUR PC

When everyone lost it at once, the cause is on the admin side

If one PC has the problem, it is the PC. If the whole office lost the library on the same morning, nothing on any of the PCs caused it — something changed in Microsoft 365, and no amount of resetting will bring it back. The usual suspects, in rough order of how often we meet them.

• The library was set not to allow offline copies. There is a setting on each library, in its advanced settings, that controls whether it can be synced at all. A site owner tidying up can switch it off without realising what it does, and every synced copy stops.
• Sync was restricted to managed PCs. An administrator can allow syncing only from computers joined to the organisation, or only from particular devices. Home PCs and personal laptops drop off overnight.
• Permissions changed. A reorganised site, a group membership removed, or a guest account expiring. The library is still there; you no longer have the right to it.
• The organisation’s own security rules. Conditional access policies can block sync from outside the office, or from a device that has not met a requirement.

All of these are fixed in the Microsoft 365 admin centres, not on the PC, and they need whoever administers your tenant. If that is a previous IT provider who has gone quiet, that is a problem we have written about separately and one we deal with often. If it is us, or you would like it to be, this is a short remote session: we look at the PC side and the admin side together and put the library back where it was.