Slug changed after being published?

I have two posts with slugs. After being published, their URLs have "-2" added right after the slug. I have checked the slugs of each post and confirmed that they are not identical. This leads me to believe that there might be another reason for the addition of "-2" in the URLs.

Here is one of the post has a slug "bionic" but it's URL is displayed as being "bionic-2": https://kuoyihs.in/bionic-2.