Word for Mac on NFS share thinks documents are read only

I have a strange issue with am Unraid server running NFS shares.

Facts:

• Running a fresh install of Word on a fresh Mac on a fresh Unraid server
• Documents are on an NFS4 network share
• The share and documents has all permissions: Read - Write - Execute
• I can verify this by using "Get info" on a Word document and see that myselv, mygroup and all users has Read and Write. I can also verify directly on server. Documents are 777 (rwx for all)
• Ready only is not set on document (as seen from Mac get info)
• Locked is not set on document (as seen from Mac get info)

Symptoms:

• When I open a document located on the share in Word on the Mac - it displays a message that the document is read only and only gives me the option do duplicate it. I can duplicate it fine and save to the network location, but when opening the duplicated document, I get the read only message again.
• No other programs are behaving this way on the same share - Excel, Powerpoint etc works fine. I can even open a Word document in a text editor and are able to save it - so if it definitely not read only
• If I create a new Word document and saves it to this network share - I get the same behaviour - it gets read only
• If I map the network share using samba (SMB) protocol instead of NFS, it works fine - issue is only with NFS (but I prefer NFS due to speed & reliability when there are many files)

So somehow Word thinks that documents on the network share are read only - while they definitely not are read only.

Can this be related to MacOs sandboxing Word somehow? Can I turn this behaviour off?

Any ideas?