Steps to reproduce

1. Setup the Application Link between JIRA and Confluence
2. Configure OAuth in the application link
3. Use the OAuth connection in Confluence (probably with JIRA gadget)
4. Check the OAuth access token in JIRA at User Profile >> Tools >> View OAuth Access Tokens
5. Change the Base URL of Confluence and re-create the Application Link again
6. Check the OAuth access token in JIRA

Workaround
Modify the description from the database

• JIRA

  SELECT * FROM oauthspconsumer;
  

• Confluence

  SELECT * FROM bandana WHERE BANDANAKEY LIKE 'com.atlassian.oauth.consumer.ConsumerService:host.__HOST_SERVICE__';