Something similar JUST happened to me! I installed a new pair of SP41 ECO (green-etch) ACE lamps (likely a 'residential' Ecolux in disguise) and they worked beautifully for about 15 minutes before suddenly dimming and slowly fading out, at first with some faint striations/strobing. I tried wiggling them and still all I get is the cathode glow described above, which is dim as seems usual with GE Eco lamps...in a friend's basement there were/are some GE Ecolux SP65 lamps that would glow very dimly at the ends until touched (single lamp RS fixture with LPF ballast; those often have starting issues)
Anyhow, any ideas? I've touched the bulbs and they still don't light.
Or maybe the fixture is mad at me for removing the '88 Philips F40CWs that were EOL and installing these...LOL