The Jira notifications is triggered based on the enabled toggles in the Jira Notification Settings section of the Salesforce configuration.
This knowledge base will explain why you receive multiple notification for the same Jira issue.
Go to Apps > Salesforce > Connections > Configure. Scroll to the Jira Notification Settings page.
If you are the current assignee, watcher and reporter of the Jira issue, you will receive 3 notification for each trigger enabled.
Enable the notification options based on your team's requirement to avoid duplicate emails.
For more information, read the following documentation: Configuring email notifications to notify Jira users.