What can cause blurring of the entire site on mobile?

Question

Adaptive design

On mobile, when the site loads, everything is fine, but after loading, after about 2 - 5 seconds, everything is blurred, not much, but everything becomes soapy and not clear.
Unfortunately I can't attach the video.
It happens on such a layout.
It is noteworthy that everything is in order on other phones, which I suspect have a larger resolution.
Mine says 480x854, but the site looks like it's 320x480.

Answer 1

Found the answer!
Perhaps someone will have such a problem, but I doubt it.
The bottom line - I had a logo in the basement, and since it was not png but jpg, and the background of the basement was gray and not white, I decided not to bother with creating a png logo, but just mix colors through css (mix-blend -mode), that's what it was, removed the mixing of colors and made a png logo, now everything is fine!