PNG file import probleem

Hi all,

Recently, I have imported the png images into illustrators. initially it looks like below (normal)

But after i save the file as in .ai format with option below

and I re-open the that file.

It become like image below,

I have tested lots of png images and I relized that it is not because of the file, which is imported.

Do you have any idea about this?

Thank you so much for your kind help.

with best regards,

Doyoun Kim