It seems I’ve completely misunderstood the new concept behind tracklogs. Sorry!
When I switched from the old Planner to the new Planner, a subdirectory called _Tracklogs was created for me.
I assumed this was part of the new Planner and that I’d be able to find all my tracklogs there in future.
I need to go through the whole thing again, as there are a few things that aren’t working as they should.