I replaced the lamp with a new one.So far everything seems o. I did take some measurements.
The circular lamps are mad with two filaments at end. That enables them to start with old fashioned glow starters. In my case, the quick start method is used. The filaments act like electrodes. If you can start them by hook or crook you do not need intact filaments.
What appeared to have happened in my lamp was that one of the filaments opened up. Apparently the filament was still connected at one end and that was good enough. I just checked the continuity of the filaments. One was ok and the other not.
I hung the new lamp by its connector. It did not start spontaneously.I think that having the lamp in its fixture helps starting. It is held in place by three spring clamps. That extra capacitance to ground is probably important. For the few dollars a new lamp costs it is not worth tracking down the failure any further. I continue to have starting problems, I will post again.