Summary

After updating the base URL, editing any pages that were created prior to the base URL update, will cause all links on the page to turn into links to the page itself.

Steps to Reproduce

1. Create a blank Confluence page - Page A
2. Add links to other pages on the instance and @mentions to users on the instance:
   
3. Save the page
4. Change the Confluence instance's base URL to valid base url
   1. Shutdown Confluence
   2. Add a context path to the server.xml
   3. Restart Confluence
   4. Update the base URL
5. Edit Page A, not making any changes to the content
6. Save Page A

Expected Results

The page remains the same, links remain intact:

Actual Results

All the links on the page become links to the page itself:

Notes

1. The storage format for the links is identical on the page before the issue occurs, and after the issue is resolved with the links recreated correctly
2. In an instance where an upgrade was performed, all pages edited and/or created after the upgrade, and before the base URL change are affected. Pages that were created/edited prior to the upgrade, but not until after the base URL change are not affected.

Workaround

Turn Collaborative Editing Off

1. Go to > General Configuration > Collaborative editing
2. Click Change mode
3. Select Off
4. Click Change
5. Then rebuild the index via the UI

Turn Synchrony Off and On again

1. Go to > General Configuration > Collaborative editing
2. Click Change mode
3. Select Off
4. Click Change
5. Then turn Synchrony back on
6. Then rebuild the index via the UI
7. The links should be resolved

All existing shared drafts are lost when you switch to this mode, so make sure your users have published any work they want to keep before you make the change.
More information on this can be found in Administering Collaborative editing.