Yesterday I assembled 2x18W fixture from leftover spare parts I've had laying around and after getting it done inserted a one philips TL-D 18W/33 and one Sylvania luxline plus 18W 840. Both tubes were unused but have been sitting in a shelf for quite some time. The fixture is equipped with magnetic ballast with lamps in series. Starters were new philips S2. Philips lamp started okay but the Sylvania one just kept blinking. Letting it try few minutes didn't help. I replaced the Sylvania lamp with another Philips and the fixture worked fine. I was almost labelling the Sylvania lamp DoA but then I tried it on magnetic 1x18W fixture with electronic starter and..... it started fine. Then I switched it back into the 2x18 fixture and now it started there also. Then I remembered seeing similar thing before.

So the question is, why first time starting seems to be hard on some fluorescent lamps?

Newly manufactured discharge lamp needs some time to stabilize on the first run. Modern high-speed manufacturing lines may not have enough time to age the lamps completely. Physically, aging usually means residual gaseous impurities get absorbed and cathode oxide material coating gets finally activated. That means gradually lowering ignition and burning voltage. When burning voltage is too high the starter will cycle. Also, cathode activation is very sensitive and may get partially poisoned while impurities are still present and so burning voltage will be higher than normal until all impurities are consumed. And, even if new lamps get completely aged at the factory, lamp components - metal, phosphor and glass will release some gaseous impurities while the lamp is in storage - so it is typically necessary for a discharge lamp, be it a small indicator neon, or a big 5ft fluorescent, to age for some time again to stabilize after  storage.

Also, electronic ballasts and starters are typically providing more predictable starting voltage and are less sensitive to elevated burning voltage of the lamp, so it may be really preferable to age the lamp on the electronic circuit first.

Interesting. Personally I've noticed this happening mostly with modern lamps (produced within last 15 years) so I suppose the speed of production might definitely be one of the factors.

You could pull the starters out to prevent them from restriking the contaminated lamp, wait several mins for the lamp to warm up, and return them.

Interesting. Personally I've noticed this happening mostly with modern lamps (produced within last 15 years) so I suppose the speed of production might definitely be one of the factors.

Quality control slipped a lot, for sure when tube production was moved from 'motherlands', Netherlands and Germany, to third countries.

But  I think what you experienced coincided with an earlier global move from good old T12s to krypton filled T8s. This already increased ignition voltage a bit, and rapid start operation was sacrificed. But one can imagine with already high ignition voltage of T8 tubes some extra voltage rise will become  especially problematic. Also latest 'ecological' generations of T8 tubes suffer from mercury condensation and starvation, which probably adds a bit to already existing ignition problems.