How to troubleshoot 500 Internal Server Error

Hi,
I am getting Error 500 some times on my page like when I click on new post or other link. But as soon as I refresh the page it works fine again. To monitor this I activated Uptime monitoring tool. The app also reported error 500 and sometimes the error lasted for few minutes and sometimes 20-30 minutes and auto recovered.

I tried checking the error log in CPANEL, but nothing found. Contacted hosting provided (BigRock) but they are unable to troubleshoot unless they found the error live.

Thing is that it doesn’t happen all the time. How can i fix this?

Thanks