In Bitbucket, it is possible to have multiple application links to Jira. Due to this, it is possible to have a commit with a description pointing to an Issue Key which is present in more than one Jira instance. In this circumstance, the following logic can be observed - Linking Bitbucket Server with JIRA
If Bitbucket Server is linked with multiple JIRA Software instances and the projects happen to have the same key, only the issue from the instance marked as PRIMARY will be displayed. See Making a primary link for links to the same application type.
However, this may not be comprehensive enough; it is unclear what happens if the Issue Key is shared between two Jira instances for example, while a third Jira instance is the PRIMARY.
Ultimately, there is no easy way for a user to specify, or identify, which Jira instance to link a commit to in the circumstance where there are multiple instances with the specified issue key.
In the Bitbucket UI, it would be valuable to present the user with an alert or other visual indicator indicating that the Jira issue key the commit is linked to is present in more than one Jira instance.
Users may unexpectedly find commits linked in their Jira issues when those issues inadvertently share the same issue key as the intended issue from another instance. Having greater visibility of this circumstance in Bitbucket can alleviate this confusion.