Konstantin,
What size of image did you download form your site? The smaller images (for example ‘thumbnail’ or ‘medium’ sizes) that are generated by WordPress are not compressed. As of version 1.1, only the ‘large’ size and the original file are compressed. This is a change that was made in order to reduce the amount of calls to the TinyPNG API.
I solved the problem. The plugin does not compress images. Under the new boot – all good!
Konstantin, would you consider changing your review?