As you can see, the equations $ ( 1 ) $ and $ ( 2 ) $ are not shown properly, while equation $ ( 0 ) $ is. The confusing part for me is that while I was writing the answer, the preview under the box I was writing in, was alright. In fact, it still is, when I try to edit the answer:
This is the second time I have this kind of problem on MSE. I need to go through my previous post to find that one and give a link to. But the thing is, last time that this happened, I tried editing the code I wrote for the equation so that it may looked as it was intended to, with no avail. I tried putting braces around the expressions after
\label, but it didn't work. And one thing is that I've written many many posts with this style, and had no problem except in these two posts.
I want to add that I remember there was something different about the preview and the actual output of tag infos, when I was editing them a long time ago. I can't remember what exactly that was, and whether it was related to this one or not. But I think it was the other way around: the preview had problems, while the actual output was alright; so I let that alone and forgot about it, until now.
So what is the problem exactly? Is it something with the implementation of Mathjax on MSE? Is it something with my browser for example? Or what? Why is it different in the preview and in the post?
This is the other post I referred to. As @MartinSleziak suggested in the comments below, the problem was due to the fact that the same label was used for another equation in another post. This time, it wasn't in the question, but in another answer. I edited the other answer and changed the label, and everything was displayed normally after that.