When trying to export a Space using the custom export option "Error Loading Pages"

Summary

When trying to export some spaces with lots of pages and attachments, using the "Custom Export" option could be used to avoid problematic pages if the space exports fail, however, for some Confluence instances the custom export renders an error "Error Loading Pages".

Steps to Reproduce

1. Via "Space tools" browse to "Content Tools" and click on tab "Export";
2. Choose the export format and click "Next";
3. Click on "Custom Export".

Expected Results

The page tree is loaded and you are able to choose which pages to export.

Actual Results

The page doesn't load and an error is rendered in the UI.

Workaround

None so far.

Notes

Exporting to other formats could work.