This issue was reported by Erik Lattimore on bitbucket.org:

We have noticed that when the AWS snapshot copy operation between regions takes longer than the CLI wait command is willing to wait, this backup script believes there has been an error and fails to tag the copy with the appropriate name. This is problematic because it is difficult to track down where these snapshots came from w/o having correct names.

Ideally, the AWS CLI command wouldn't timeout under such a scenario but since that is a different issue, it would be nice of the Atlassian backup script was a little better in that if the wait operation timed out, it would still attempt to apply the tags to the in-progress snapshot.

While the latter paragraph is technically a suggestion (as opposed to a bug), I would still consider the behaviour that caused this report an actual bug that we should fix or provide a proper workaround for.