Can you give us the source file, so that we can see why some questions are not handled by AMC?

Of course I can (please find it attached).
Thank you very much for your prompt reply!

The problem comes from the question ID with a non-ascii character (\begin{question}{sensibilità}). Create a new project with the same source file, changing only this ID (for example \begin{question}{sensibilita}), prepare the documents, build the page layouts, ask for data capture with the scans you already get, and all should be ok now (there should not be any problem since the layout did not change, only one internal ID).

I see... So, despite loading the inputenc LaTeX package with
utf8x option (which fixes things as far as the TeX compilation
is concerned), accented characters may still pose a problem with the
rest of the process. Glad to hear that I can easily change it without having
to worry about the papers already answered.
Thank you so much!