So my previous question about when to apply the fat pixel shader is probably unrelated (my bad). The star shader never samples from the original texture. It just runs on the frag shader, calculates a star value based on a simple noise then multiplies that with a star color. It doesn't care about the texel's size or value of the original texture. The stars you see in the video are on an 8x8 empty sprite. I don't want it to sample the texel of an 8x8 sprite.
The problem is there are a couple of bright pixels in the middle of a bunch of dark pixels which will be applied a bloom effect on a post-processing state. Because the camera is moved by a SmoothDamp function so when the camera gets close to its target then these pixels get flickering (and it's noticeable because there're only a few of these bright pixels). But I don't really know why the pixels get flickering and is this problem related to the "fat pixel" in any way?