Hi. Thanks for your report. You may want to [url=https://support.steampowered.com/kb_article.php?ref=2037-QEUH-3335]verify the integrity of your game files[/url] in the Steam app to see if that helps with your issue. You may also want to [url=https://support.steampowered.com/kb_article.php?ref=3134-TIAL-4638]clearing your download cache[/url].
Have you already completed final blows? I wouldn’t worry about the medals so much. For most people, the final blows will take much longer, and the medals will be complete far before the final blows. That said, it would be hard to substantiate your claim without a video as proof.