@katmarczyk - This is a bit strange as there was another post a few hours ago that sound similar. A few quick questions.

When you open the board and click/tap on the board title, does everything look as expected, e.g.:
 

And what options do you see when you click on the locked object? E.g., I see this:

One last question: Are you for sure viewing the board while signed in? This may sound silly, but it would be possible for a board’s sharing settings to be set to Anyone with the link → Can edit and you were viewing that board as a guest editor, which cannot lock/unlock objects.