Split-by=timings not splitting evenly

I’m splitting by timings but I’ve noticed from the Timings tab that they are not evenly split. I could be done my suite in around half the time if it wasn’t running so many tests on run #0

I’ve tried renaming the path (store_test_results: path: test_results2) and increasing parallel runs to bust the timing data cache but it always seems to overload run #0.

I’ve also noticed that run #0 has the same warning about the same 2 files on every run:

No timing found for "spec/models/notification_spec.rb"
No timing found for "spec/models/related_document_spec.rb"

Is there a way to nuke the timing cache so that it’s like it’s running parallel for the first time? Or is there something else going on that’s getting in the way of an optimal split? A recent refactoring significantly brought down test times in series from ~42 mins to about 16 mins.