Translation doesn't appear

Hello WPMU DEV Team!

I finished WP Smush translation this week and today I've done some tests.
I've downloaded translation files (po,mo )from https://premium.wpmudev.org/translate/projects/wp-smushit/pl/default and uploaded them on one of my sites (wp-content/languages/plugins).

I've found out that for some strings translation doesn't appear.

1. Page title (Browser tab - in my example Chrome)
2.