Exactly, improving the start time would greatly improve this feature.Time Stretch is based on Start Time so calculating it is critical, so at this point we'd need to improve Start Time which will in turn make Time Stretch better. Sometimes it doesn't take into account "Override previous track mix" point correctly, maybe this is the case?
In this case, none of the tracks were a file type, so it's strange.
Unless the Time Marker has some effect.