If you look at your [reputation tab](https://mathoverflow.net/users/94729/emmanuel-jos%c3%a9-garc%c3%ada?tab=reputation), you can see two events for today: upvote +10, and unupvote -10. In general, [the reputation tab](https://mathoverflow.net/users/current?tab=reputation) and [the reputation breakdown](https://mathoverflow.net/reputation) provide more details than [the achievements dropdown](https://meta.stackexchange.com/tags/achievements-dialog/info).

[![Screenshot][1]][1]


These two events cancelled each other out - in total your reputation did not change. As far as I can tell, this is the reason why nothing related to this post was shown in the achievements dropdown.

On Meta Stack Exchange you can find several posts related to this - including some feature requests saying that some users would prefer to see the negative reputation changes, too: 

 * [Why do reputation drops not highlight the Achievements icon?](https://meta.stackexchange.com/q/219652) 
 * [Display lost/negative reputation in topbar achievements](https://meta.stackexchange.com/q/208900)
 * [Please consider displaying reputation decreases in the Achievements trophy icon](https://meta.stackexchange.com/q/350358)


  [1]: https://i.sstatic.net/0eQJ5.png