External 4K monitor shows wrong resolution

I bought a Philips 288P6 4k-monitor and plugged it to my Retina MacBook Pro 15".

For a few days it worked just great. When selecting Scaled instead of Best for Display, it gave me the retina style selection of More Space etc.

Now, today when I again hooked up the screen to my MacBook, the display showed an awful 1080p resolution. When I go the System Properties > Displays and select Scaled, only 1080p and bunch of lower resolutions are shown.

What's up with this and how can I fix it?