Hello Sheaxumea81
Try entering all data in full capital letters.
It can also be that there is an inconsistency in the timetable due to wrong programming of the timetable; this is not uncommon with Trenitalia due to their countless number of engineering works they have planned on their network for this year.
As travel experts, we do recommend purchasing tickets with the train operator that will be operating the line, or if multiple operators are involved, with the first operator; in your case this will be Trenitalia.
If you book with another train company in Europe, you will simply add complexity to your booking, which can become a great issue if you face cancellations or rebooking due to timetable changes and delays. It is much easier to talk to an agent at the station in the country you are, then to call SBB from Italy to change your booking for a trip in? Italy! To avoid data traces, you could use anonymous e-mail addresses, whatsoever.
Kind regards.
Roland