Custom query AFTER rss fetch_feed not working

The error seems to be connected to the rss url itself, if I use ‘http://seko.se/feed.rss?rssId=97‘ I can’t create new loops beneath it but if I use another url such as ‘http://www.wpbeginner.com/feed/‘ It works.

My original feed works just fine in other readers so I have no idea why it does not work in wordpress.