i have a wheelchair bound toilet in my school where the light is facing the exact same issue. the starter has been stuck for a few months already and the light is just left in this state 24/7. the ballast as also buzzing REALLY loud, like a motorcycle on full speed. eventully the poor little magnetic ballast violently burned out and the light was replaced with an led.
I just got a fixture like this it has a 72w ballast for the 2 36w bulbs and when I turned it on one of the bulbs started flashing and the other one had a dead starter
This is used be scary af for me when I was small. One night at around 1am I wanted to go to the toilet, no lights were turned on, and then I saw a desk lamp (T8 15W) doing this.