Thanks for this thread. I can definitely say that here are the most important 2 points that might interest you!
1. The screenshots are generated when you go to a page in Edit mode and do a change there. The system then fires an event and our screenshot service takes the latest screenshot
2. In some cases these page thumbnails are used as an Open Graph images when posting the page to the social media. When you update the OG image of a specific page from the SEO app, the system overrides the page thumbnail immediately.
I will pass this to the product team to check if there is smth wrong with your website that stops new screenshot to generate.
Best of luck,