Why! What's this?

Why ?

Stop Move:

When I moving: What is this?

Hey there, is that just an image in a UMG widget? Try setting the scope texture to No Mipmaps and on the compression settings set it to UserInterface to see if it helps.

Not use UMG widget, but I still try setting texture NoMipmap and compress mode, no effect.
I only put a plane with below material at camera forward.

I would probably do it with UMG, you shouldn’t have those problems.