Dear Yannick,
I'm working in this web site with last Joomla and Sh404sef version:
https://www.xxxx.com/anto296/
In the footer I added a new item voice called "Ricette primi piatti Test1" or something similar.
Its link was: https://www.xxxx.com/anto296/ricette-di-primi-piatti.html
Then I decided to deleted this item voice from this menu and to move it to a hidden menu called "Nascosto ricette". Then I added to this new item voice the same alias: ricette-di-primi-piatti
Problem: the link doesn't work. Thus I went to Sh404sef and to "SefURLs" --> I found "ricette-di-primi-piatti.html" and I deleted it.
Then I check if the URL https://www.xxxx.com/anto296/ricette-di-primi-piatti.html worked without success.
I'll be gratefull for your help.
Thank you very much.
A nice evening
Andrew