image got pixelated on ios device

(Sorry for bad English.. my mother tongue is Korean..) this is captured image from my game.. on background(black one) image, it looks kinda pixelated and font is floating.

This is shown for a moment. like 1sec?

1. using screen filter(with shader)

2. text - Text Mesh Pro

3. image - nothing. It sets to 'none'. No material

4. iOS Device

I'm suspicious of screen filter shader.(It renders Main Camera) But still, I can't find cause.... help me ! plz