WordPress Single Post Feed Not Working

Hi, I need help to sort my all single post feed url not working and generating 404 error. I came to know this from Google Webmaster Tools. There I found lot of not found and all the not found url are like this: https://www.mydomain.com/samplepost/feed

By the way I have changed with the default theme and disabled all the plugins but could not resolve the issue. My normal blog feed and comment feed are working fine.

Here is my blog url: https://www.online-learning-guide.com

As a live example of one of my blog post https://www.online-learning-guide.com/building-a-healthy-church-congregation/ is working fine but the comment feed of this post which is https://www.online-learning-guide.com/building-a-healthy-church-congregation/feed/ giving 404 error out put. Please help to fix this error.

Thanks