We had few issues in past few weeks where backend-redis was missing metric keys after a manual Redis sync.
With the latest customer which came across the issue had only one metric which did not sync to Redis database after following all the steps in the KCS.

The support team would like to understand which metrics(Product , Backend) are synced to Redis, when sync is triggers BackendStorageRewriteWorker .

We can see that the rewrite_provider function is supposed to sync metrics that either belong to a service or a parent according to this line. If we understand this correct that means both a metric which belongs to a Product and a Backend API should be synced but we have seen twice now when resyncing data to an empty Redis that metrics are not (or at least not all) synced.