Understand the number of messages dropped due to RouteBackNotFound

[bowenwang1996]

We often see, in both single-sharded network and multi-sharded network, that some messages get dropped because its route back cannot be found. We should first understand the number of the dropped messages and then decide how to proceed. There is a PR #3088 that should address the issue mostly, but it may take some time to finish and we may need to revive it if a significant amount of messages are lost due to the route back issue.

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[stale]

This issue has been automatically marked as stale because it has not had recent activity in the last 2 months.
It will be closed in 7 days if no further activity occurs.
Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity in the last 2 months.
It will be closed in 7 days if no further activity occurs.
Thank you for your contributions.