Generative Extension simply not working

I have been trying the Generative Extension tool, and having zero luck. Every single clip reports back "could not generate extension" after the progress dial reaches 100%. I have confirmed that the clip meets all the technical requirements:

• 16x9 aspect ratio.
• Square pixels
• 23.96 fps
• Several seconds of footage before the end.
• Good network connection

Is there a way of getting a report or error log with more detail as to why the extension failed?