There is various things.
I use WPML “String translation” which, when activated, give an memory alert when I try to create a new menu (for example). I put my php memory limit to 512 Mo but it always give an alert. I ask for that to WPML support.
When I upload a new theme legenda, it’s ok.
So I create a child theme with a very few files, and custom.css in parent theme, and .mo files in parent theme/languages.
After 5 minutes, the mobile menu become inactive.
When I destroy child theme and custom.css, the mobile menu is still inactive until I upload a new Legenda. ???
I’m searching the exact point for that.