Attention
Please notice the Smart Commits documentation informs the issue key must be used in uppercase letters.

When a commit contains a JIRA issue key in its comment and the commit is added to a review, Crucible suggests to link the review to the JIRA issue mentioned in the comment.
If the issue key is in lower case, the creation of the link will fail, with the following message:

JIRA Server JIRA-6.2.7: This issue does not exist or you don't have permission to view it. Go to 'JIRA-6.2.7' or see your administrator.

Resolution
Despite the recommendation of the document first mentioned, it was checked this works in the most recent version of Crucible.