Issue Summary

HTML export of a Confluence Cloud space fails when the space contains pages with <ac:image><ri:url> tags that reference internal wiki image paths (e.g., https://<tenant>.atlassian.net/wiki/Images/image.png). These image references are typically leftover from Server→Cloud migrations. The export aborts entirely on encountering such a page, preventing the full space export from completing.
PDF export of the same space is not affected.

Steps to Reproduce

 1.  Have a Confluence Cloud space containing a page with an <ac:image> tag using <ri:url> referencing an internal wiki path, e.g.:

<ac:image ac:height="96" ac:width="288">
  <ri:url ri:value="https://<tenant>.atlassian.net/wiki/Images/unlocked.png" />
</ac:image>
 2.  Go to Space Settings → Content Tools → Export
 3.  Select HTML export and start the export

Expected Results

The HTML export completes successfully, either exporting the image correctly or gracefully handling the unresolvable image reference (e.g., rendering a placeholder or broken image tag) and continuing the export.

Actual Results

The export process starts, gets stuck, and then fails with the generic message: "An error occurred during export."
The below exception is thrown in the application log:

logger: com.atlassian.confluence.importexport.impl.HtmlExporter
message: Entity being exported was: page: <pageId> v.<version>
logger: com.atlassian.confluence.importexport.actions.ExportSpaceRunner
message: Error during export for XML UI
Caused by: java.lang.StringIndexOutOfBoundsException: Range [-1, 25) out of bounds for length 25

The HTML export image rendering pipeline encounters the ri:url reference, identifies it as a Confluence resource (because it starts with the tenant base URL), and probably attempts to resolve/convert it to a relative export path. 

Workaround

Perform a custom HTML export excluding the affected pages.

Alternatively, the customer can edit the affected pages and remove or replace the broken <ri:url> image references with properly uploaded image attachments