Hiya welcome to Netlify’s support forums! Sorry to hear you are having issues with your code. I’m assuming this is not working on you local machine? Unfortunately, debugging code is outside the realm of support.
We do have these support guides to debug your build, and of course I will leave your thread open so other community members can help.
I checked your site and based on your build logs, I can see /courses is an ISR path. From our logs, that appears to be revalidating and working fine. If you feel it’s not working, kindly add a date-time somewhere on your page so both of us can see if this is working incorrectly or not.