About Mario Rossi, it feels natural to me that it appears for me because I'm Italian :-D
To find the bug try the following steps:
1) Play the game from itch.io and not from Construct, you might have touched the code somewhere in the uploaded version.
2) Sit with friends and family members, let them try the game without explaining anything about it. See how they play and if they get Mario. It might be that we try a combination of things that you don't do it because you made the game and you know exactly where to click and drag things.
3) Try to put envelopes in the drawer, remove letters and photos from the envelop, and drag those on the interactive areas, that might be the thing causing the trigger.
4) Add logs to the code to track what's happening with variables and such, you might notice something weird.
I know about the deadline, I had I 9 more hours, but for me was time to sleep, so I did a last bugfix causing at least two more serious bugs and I found it out the day after, once the jam was concluded! :-(