Ray Tracing

Both motion blur cages and global motion blur work in combination with Raytracing.

However, mixing rasterized translucency with raytraced translucency is not supported yet (at least as of UE4.25)
Because of this, Translucency should be set to Raster, instead of Ray Traced.

Next, you might encounter the following issue:

The image inside the cage is too dark, and it casts a shadow. This can be fixed as followed:

Find the blueprint named BP_MotionBlurCage. This is the parent blueprint to all blur cages. Double click to edit.

In the Components panel on the left, select BlurCage. In the Details panel on the right, find Visible in Ray Tracing and disable it.

Now the image should look correct. This will fix the issue in all motion blur cages across all scenes.

In order to maintain project version consistency, and due to possible changes in the UE4 raytracing implementation, I will not include this fix in the version on the UE4 marketplace.