Modern Vespa

Hi
Most times recently, when I hit the starter button, instead of the bike firing up , nothing at all happens and all the dashboard lights die and the red immobiliser comes on as if the key had been moved to Off. If I turn the key off and on and repeat, it might start or the dash might die once again. Once it does start, usually after say 3 gos, it stays running fine and rides ok - except for two stalls while moving but which haven't recurred recently.
I first suspected a bad "mechanical / key position" issue but I now think it is electrical, but I can't think what would cause the dash to go off in this way - it's like the operation of the starter circuit causes a short circuit that kills the ignition circuit (ie sets it back as if the bike was totally switched off).
Thoughts?

What shape is the battery in?

Check your earthing connection to the engine.

I was assisting / observing my Vespa guru do a clutch deglazing on his HPE.
He had an intermittent problem of not wanting to start after a wash.
We found that the ground wire had parted company with the lug at the crankcase end. Replaced and fixed.

I'm going with battery. I recently had a very similar issue but not with my Vespa. My 2018 Jeep Renegade suddenly would not start and the dash would do all sorts of things, giving me messages that made no sense. A new battery cured it.

Oh, BTW, the Jeep was made in Italy.......

THanks everyone - I think that the battery being slightly below some given voltage is the answer.
I am guessing it is the original battery in a 2016 bike which I bought with very very low mileage. I'll check tomorrow.
Combine that with (unusually) not riding it for a week and it's easy to see why the issue could arise. Funnily, after posting today., I decided to clean the kill switch and starter buttons with contact cleaner. But before I did, I found I couldn't recreate the problem (because I had ridden it a good few miles today so voltage was up!)
Thanks for all replies I hope this helps someone else too!

Hmmm - still happening. The scooter has shut down while on the move twice in the last 24 hours!. Shuts down the engine and the dash goes dead as if it was switched off with the key. That sort of suggests the battery is not at at fault- it measured 13.5 volts the other day and starts happily and turns over quickly etc. It's also surely unlikely to cut out when running.
The only variables are that it's damp weather here and near freezing.
Any thoughts on where the failure point might be - presumably some poor connection/s - ignition switch? main multi-wire connectors? Other?
Thanks

What I can add is that on the still rare occasions when this problem arises, the ignition is switched on and the dash lit up as normal, applying either brake - before hitting the starter button - causes the dash lights to die and everything to shut down.
So this narrows things down. It is NOT the kill switch or the starter button (and almost certainly not the battery) because it happens before the starter is pushed so there is no "load" on the battery.
So, pulling in either brake lever causes the problem. Jiggling the ignition switch while holding the brake in can revitalise the dash and the ignition. So I'm pretty sure I can blame the ignition switch. The question now is whether it's mechanical or electrical at the ignition switch! Any experiences out there?

Brake lever being pulled should activate brake light causing a load to be applied to the battery. Appearance of loss of all power when pulling break lever would have me looking for a poor electrical connection. Could be ground or positive connection, poor connections often are difficult to pin point.

I think it's solved. I took out the electric part of the ignition switch and , on the bench, sprayed it through every orifice with electrical contact cleaner while operating the switch repeatedly. It seems to have solved the problem and that approach seems to match the symptoms!