Some more info about the anti aliasing jitter is in the documentation of UE4.
This has to do with in what order effects are applied, solved in this post:
Depends on how the post processing is implemented , probably it checks for certain angles, edges or shapes on the texture to calculate outlines for. You could apply the post processing only to certain meshes (sky, land etc) by creating a depth stencil mask as done here:
This is probably a reroute node. when you drag a pin to create a line, release drag and type “reroute”. You should consider using one of the blueprint plugins which automate the placement of lines and nodes to not lose time on the BP interface like that.