Hello,
yes from your description it looks like a problem on routing of URLs....
by the way when you use precaching you don't have to move any files, they are stored on a cache server folder but are managed automatically.
You have to submit always the same link for the sitemap,
https://www.mydomain.com/nl/component/jmap/sitemap/images
then it will be the component that will use the precached file instead of generating the sitemap in realtime.
If you have issues using SEF version of links you can safely use the raw links as by default.
John