Diana, it doesn't have anything to do with Yoast. Take a look, I've disabled the plugin and the page title in course pages is still missing in front-end, although the course has a page title in back-end. It needs some filter to force back the page title. Please, make a small effort and provide a fix.
https://prnt.sc/rfowxd
regards!
No, it's not, the issue is still there: https://prnt.sc/rj44ij
What's exactly did you do? Please, read again my first message, maybe there is something that you didn't understand. You can deactivate the Yoast plugin to check it that way, but the <title> tag looks the same.