Bad gas. There are a few independently owned stations around and buy gas wherever it's cheap. A few years ago one station bought a load of gas that was laced with industrial solvents. A few cars ended up with seized engines. Shouldn't be a problem at known brand stations.
I had a car that did the same as the OP's bike but it had points and the rub block was worn. It needed RPMs to float the points a bit so stalled at idle. I assume the bike in question has a more modern ignition system.
I had a car that did the same as the OP's bike but it had points and the rub block was worn. It needed RPMs to float the points a bit so stalled at idle. I assume the bike in question has a more modern ignition system.