“blue edge” and “vapour trail” are 2 different things. The former I’m explaining in a post above, the latter is because of the use of an accumulation buffer (or something working similarly to). The former is because clouds are most likely rendering after the rest and the shader is using the depth buffer to know where to draw clouds in the image, but this makes it challenging at the edges, the latter is because it is an optimization technique to spread heavy shader computations (clouds) over a number of frames instead if 1.
You can see the latter very clearly in VR (didn’t try in 3D) in using clouds ultra with weather displaying lots of big and small clouds with complex patterns for example, then in flying fast above them at 40000ft. Try looking at the clouds and see how the closest ones moving faster relative to the aircraft are building incrementally from bigger white cloud boxes (ala Minecraft - voxels) and hit ESC to see how they become much clearer and highly defined at the edges in an instant. Press ESC again to resume and see how to fade to building boxes again.