The problem could have different reasons even depending on the server itself, it's not possible to determine the exact reason without having a look.

What you can try to do is reducing the links analyzed for each precaching step using the parameter in the screenshot.
Also excluding some data sources can help you to understand if there are some of them generating a server error.

Here is a video tutorial for images sitemap configuration: https://www.youtube.com/watch?v=lTvnoiFXPKk&list=PL6t5xIMeFJ2JG3OQASXPLi5YrFduVGWq3&index=1

Best regards
John