[REG 6.2.4 -> 6.5.3] "Classes" page is empty

1. Start Assistant.
2. In the "Contents" view, expand "Qt x.y.z Reference Documentation".
3. Click on the first child node which appears: "Classes".
   The main view will show a blank page.

Instead, this should show a list of Qt's classes. This works correctly in Assistant from Qt 6.2.4.