What does Stryd's offline sync update change?

It matches pod-stored runs against watch activities automatically, assigns a match badge and recommended action to each, and merges Stryd Duo balance metrics into the watch activity where COROS, Suunto, or Polar watches are involved.

Why did Stryd's offline sync cause duplicate runs before this update?

A manual pod sync could upload a second, separate activity alongside the one already saved from the watch, leaving two incomplete records of the same run rather than one complete one.