Great, so in the process of unsuccessfully attempting to copy timelines from one project to another, I must have borked the existing timelines I already had in the main project folder without realising it.
Just went to work on them then, only to find that although they exist in the project view, when clicking on any timeline, the objects and paths have all been deleted.
...
Now I really want to know how to copy timelines from one project (my old archived copies where they still exist) to another (my newest iteration with zero working timelines).
Surely someone will have an answer to this?