Modern Vespa

I have a 2017 Primavera 50 (low miles <150) that starts fine and runs well under throttle. At temperature the engine stalls at idle. I do hear ticking noises from the ignition coil before it dies. Spark plug is new, wire connections are good and wire is in good condition. Scooter has been sitting for a while. Fuel system was serviced by dealer (all new lines). Bad ignition coil?

Step 1: check battery (including while the engine is trying to idle).

When you say the dealer fixed the fuel system - did they adjust the air/fuel mixture for best idle when the engine was up to temperature?

Yes, they did. It ran fine after the fuel system service by the dealer. The stalling started recently and is getting worse. I am not sure it is related to ambient temps (we have had 90+F days).
It certainly seems like the ignition is cutting out. The coil is solid state, so I am not sure I understand why temp variations would cause issues. Perhaps problems with the spark plug connector expanding and loosing a good connection, although it seems snug.

Try watching the coil, while running, in the dark to see if spark is jumping to ground. Also, make sure the coil tower is clean and grease-free (assuming you have a conventional coil).