I've updated all amboxes on the Italian Wikipedia to use flexbox instead of tables. They work just fine in the desktop version, but Minerva doesn't seem to be able to handle them correctly. You can check this page as an example; you'll notice that the icon overlaps the text, and the text of the warning is truncated. The "Learn more" link is also not displayed.
I don't really know how Minerva's logic for amboxes works, but this seems to be caused by the new version of the template not using tables. If you go to the same example page and edit the HTML manually, replacing the outer <div> with <table><tr><td>, it'll start working again. In fact, it looks like the relevant Minerva stylesheet explicitly targets table elements; for instance, the font-size rule is only applied to td elements.
AFAICS, the new version of the template, just like the old one, follows all the recommendations for mobile-friendly amboxes, which say nothing about tables.
Check the page issue shows on https://en.m.wikipedia.org/wiki/Lody_Kong like so: