Microsoft project management software used to plan, manage, and communicate a project schedule and other information among workgroup members, project managers, and other stakeholders.
Ruairi,
It sounds like you connection to the file on One Drive is experiencing glitches that is corrupting the file. If you can open any version of the file, save it to your local hard drive. Then I suggest you do some file cleanup by saving the file as XML and re-opening the XML file in Project. Note, you will lose any custom formatting with this process.
Hope this helps.
John