A Microsoft file hosting and synchronization service.
So with Malwarebytes seeming a common demoninator in many case, I went digging on their site and it seems there have been issues with one of their components. It has only just been updated and is supposed to fix the problem. I have just updated and re-installed OneDrive so I'll see how it goes.
The MWB forum link is here: https://forums.malwarebytes.com/topic/233080-malwarebytes-interfering-with-onedrive-backup/?tab=comments#comment-1256543