Did you change anything with the default typoscript of the sitemap?
Normally https://www.lumedis.de/sitemap.xml would be an index of sitemaps, the limit of 1000 is "per page" so you would have 2 pages of sitemaps in your index.
But when I visit your sitemap it doesn't show the index but directly all the urls.
Take a look at the sitemap of typo3.org, it shows 3 pages of news: https://typo3.org/sitemap.xml
Each with a limit of 1000.