Viewports don't have postprocessing

I was messing around with some custom material expressions and afterwards I noticed that the editor viewports seemed dimmer than usual. Closer inspection revealed that also AA and almost all post processing effects (e.g. motion blur) weren’t visible anymore. I checked the viewport settings and made sure that all post processing effects were enabled and restarted the editor twice and also removed the object using a custom material expression, but the problem persists.

In standalone export everything renders correctly. Is this an editor bug?

Seems similar to this issue: https://answers.unrealengine.com/questions/86236/play-in-editor-has-low-quality.html

It was an issue with the scalability settings: https://answers.unrealengine.com/questions/86236/play-in-editor-has-low-quality.html