Read Only (Padlock Icon) files - OFDB 17.3.6743.1212

I had the same problem with "padlocks" showing in the ODfB folder, with none of the fixes proposed here or on other forums resolving it. No columns were mandatory, check-out was off etc.

After some testing I found that one of my custom columns had become "secretly mandatory".

I had added a Site Content Type containing a Required column to the library, but later on had changed it to Optional. It appears that the column was still defined as Required in the library itself!

I simply deleted the column from all content types in the library, and then also from the library itself - and that fixed the problem! The locks disappeared in OneDrive almost instantly.

Naturally, a better approach would have been to repair the column by changing it's properties with PowerShell.