Hello German,

the image sitemap can take up a lot of time and several minutes to get generated because it works as a crwaler that index your site searching for images. If you have a lot of links to scan you need to limit requests using the setting in sitemap configuration 'Images sitemap requests limit'.

This let crawler finish before server timeout.

If you can change the server timeout setting, you can rule the crawler to index more images as possible.

Best regards

John