Weird artefacts when using the Cine Camera


I’m trying to render some meshes made from particles with Niagara. The ultimate goal is to render high quality images so swiftness is not important for me.
A big part of the look I’m trying to achieve is a very narrow focus range where only a small part of the scene is in focus.
I’m using the cinematic camera with a very low f-number to achieve this.
Unfortunately there are these artfacts appearing mostly on the edges of the image:

Does anyone know what causes this and how to get rid of them?

Thank you very much!