Zerocento would be a series 1 based car. In sport mode the shift indicator will flash around the red line. In normal mode, the gearshift indicator tends to tell you to shift to be more economical. On later models it was relocated to the TFT dash so its less in your face the whole time. Only the series 4 (2016>) have a down shift indicator to my knowledge.
From memory of my '59 Esseesse:
In normal, if its flashing and you lift off accelerator it will stop, sort of as to say I'm not going to tell you to shift up if your slowing down. The moment you put your foot back on the accelerator it resets and will start to tell you to shift up again. If you let it flash but maintain current speed or accelerate it stops flashing.
Gearbox wise I'm not sure. When you say stuck do you mean you couldn't take it out of the current gear or you couldn't get it into the new one? Something like that I'd probably try it again a few times and if it plays up get the dealer to investigate. I might have had an issue selecting gear a few times and put it back into the previous gear and tried again and it was ok.
Zerocento is a very rare special edition, with only 100 made from what I can tell. The Abarth 695 Biposto Rosso Officine had 99 and the 695 Biposto Record was 133.
