Ok this was bizarre – we had a customer who had multiple machines where OneDrive for Business would not startup.
They swore that it was working fine. Never trust an end user.
The fix was to reverse a registry key which had disabled OneDrive, which in itself proves the users had no idea what they were talking about. Some administrator had rolled out a registry key to disable OneDrive, so there is no way it could have been working.
Always take what an end user tells you with a grain of salt. Like: a very very small grain.
Here was the fix to reverse the problem: Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\OneDrive.DisableFileSyncNGSC set value to 0
You are welcome =)