I have recently gotten this issue where the posts of the site I am working on does not display the comment section.
I was thinking it was caused by a plugin conflict but it turns out the solution is pretty easy and straightforward.
#1. First, make sure that comments are enabled by checking the Allow people to post comments on new articles option in Settings > Discussion.
#2. If the option mentioned in the first step is not enabled, and you have just enabled it – the comments will still not show up in the post because the discussion setting in the previous post are disabled.
#3. Go back to the posts and edit one of them then click on Screen Options which is on the top right area of the page just below your username.
#4. Enable the Discussion option.
#5. Scroll down the page and you should see the Discussion metabox and the Allow comments option under it.
#6. Enable Allow Comments.
The comment section for the post should now be available if there is no other issues causing it to be hidden.
And oh, just a quick tip. I use Chrome and I was a bit startled that when I click on Screen Option, there are not option available.
I initially thought it was a theme issue that blocks the options to be available so I switched to the 2017 theme and I got the same issue.
I tried checking on Firefox and the options are there.
After some googling, I realized it is the AdBlocker extension that was causing it.
Just disable the extension and the options should be available on Chrome.