When you clicked a notification who commented on your post, it says "this comment no longer exists"

When I was waiting for answers, someone commented on my post with an interesting explanation, but when I clicked it says "This comment no longer exists"

I was wondering what's the cause because it happens often whenever someone commented on my comments and posts, and doesn't specify anything why, like did the user deleted it? Did the mods deleted the comment, or it was a bug?

Their comment is related to the topic so I don't think they deleted by themselves or the mods, because their comment is relevant to the topic neither breaking the rules. It's just gone without any reason.