How to reproduce it :
>with the demo repository : https://demo.ametys.org/fr/espace-membre/mes-actualites.html

• the submit button works but use an old method.
• the is 2 submit buttons

Jquery 3.0
https://api.jquery.com/size/#size

In the source code of the html page of the demo, I saw other use of the .size() method (senbymail for example)