No stereo sound in Headphone when mixing with Studio One 5


I’m using the UR22-C in combination with Studio One 5 form Presonus.
When i’m mixing over the monitorspeakers, then it gives a fine and clearly audible right and left sound. But when i want to hear the mix back by headphono there’s only a mono sound!
Changements by single track from left to right are not audible in my headphone.
He used to do this before, it’s been a few days that this has now changed.

If I listen to Spotify through headphones, it will play in stereo!

Anyone have an idea what I’m doing wrong? The mix knob is set to 100% DAW