Motion blur artifacts

Hi,

I’m having some issues with the motion blur of our game. It is creating some weird sharp dither-like artifacts that are really noticeable in large screens. The stronger the effect, the worst the artifacts.

Here is a screenshot showing the issue:

Detail:

Images without compression: Imgur: The magic of the Internet

Another screenshot showing the issue even more clearly:

https://forums.unrealengine.com/filedata/fetch?filedataid=157759&type=thumb

Can you help me solve this issue? What causes this?

Thank you!