Offline files fail with "Access Denied" but only by MS Office apps

Question

I have a Win10 computer on a domain. It can access all files/folders on a server share fine when online. I have marked a subfolder for offline use on the laptop, and synced.

I can browse the offline folder fine when disconnected using file explorer, but when I try to open the Word/PPT files shown in the explorer by double clicking (launching the app) I get "Access Denied. Contact your administrator" from the app (Word/PowerPoint).

The files and folders on the server are all set for full control by everyone. The share on the server grants full control to this user.

Strangely, if I create a notepad TXT file in that same folder then I can open it fine from offline folder using NOTEPAD, sync the file, etc. All great. But MS Office apps fail to open office files only when offline. (When online they work normally)

If I open WORD when offline and click file open, I can type the "\server\" into the address bar to start browsing the offline share, however, I immediately get a "Windows cannot acess \server\" error. If I repeat the above in file explorer it works fine.

I have reformatted the offline cache and rebooted. No difference. I have repaired office 2016 installation. No difference.

What is going one here? Feels like a permissions error but I can't see it. Why office apps can't even browse the offline file structure is beyond me.

Solution

I found a clue on a microsoft forum here. There appears to be an issue related to pre-installed office on OEM computers, combined with joining a domain after office is installed.

Repairing office is not sufficient. You have to completely remove office, then reinstall. After that offline files work fine with office.