Ok, so that’s a good cell - or should be. We can probably assume that one or both chargers you’ve used are charging correctly, but have you actually used a multimeter or something to check the voltage of the cells when fully charged, and after resting awhile to be sure they aren’t self-discharging?
It’s not that nobody believes you, by the way. It’s just that with 14500 cells there is necessarily a wider margin for error and bad cells. It’s only been very recently that we’ve had these few models that can deliver some good energy like their larger 18650/etc brothers. It’s always possible to get bum cells for one reason or another, and since we’re dealing with a voltage indicator, the power source is what needs to be confirmed first. Lots of light manufacturers react just like Sofirn did and just say “try battery” right away, but often it’s the reason. 
Also…red light indicating on turbo or not?
No, it’s not normal for that warning to go off on a fully charged cell that is capable of the current needs and fully charged. That assumes good electrical design also, as well as clean electrical contacts, etc…of course. We don’t always get the good electrical design with flashlights (budget or not). I mean look at Wurkkos so far. As nice as their lights are and despite the good attitude they have shown us, a few of their lights have issues such that they just should not have been released for sale until those bugs were fixed…but the lights still work. There’s a difference in culture when it comes to “works” or “good enough”, too…some companies will bend over backwards for customer complaints and some are more choosy. Sofirn seems a little inconsistent there now that they are well established (but they are also never charging us much for the lights, and charging that bit of extra would help to cover warranty/satisfaction returns or exchanges…something that tends to get better with companies the more money you spend/more profit they make).
Now, whether a glitch is a problem enough to put a light in a narrower definition of “defective”……often with budget lights it isn’t, or at least not at first with folks that respond to customer issues after the sale. Like…ever try to deal with Banggood on a clear problem? lol.
So…curious as to why the voltage is indicating low on strobe. If it’s on turbo, too, then that’s helpful to know. We do know that turbo takes a little over 3A on this model (I don’t think anyone has measured current in strobe modes but it should be similar, possibly a tad higher). So the H10 cells if they are healthy should be fine (even though you just bought them and from a trusted supplier, the only truth teller is actually measuring their charged voltage and monitoring their resting voltage for stability…every cell, every brand). If the power source is truly good and no mechanical issues with a wonky buttontop weld/cap or dirty contacts, then it’s probably a glitch in the driver hardware (components or design) unless they bumped up the low threshold in response to customer feedback to a point where these high modes can trip it briefly.
But the most important thing about this low voltage indicator is not what it’s showing you in strobe mode…it’s that the low voltage circuit is reading at a correct low end level to let the low voltage protection circuit cut off power. You do need a way to measure voltage to confirm that and any $5 multimeter will serve that purpose. Once you’re sure that’s there then you can not worry about this as a safety issue and remain curious about the weird strobe indicator behavior while enjoying a light that works.
Sofirn isn’t perfect and they’ve changed a little over the last couple years, it seems, but they’re very good and mostly very agreeable folks. I’m not defending them or their decision here, just throwing it out there from experience and hoping you understand what their thought process might be for “defective” and this light in particular. I know a better explanation of what’s happening in the light would be great, but it’s possible they can’t provide that, or that since the light is working they don’t want to invest in tracking down and correcting a bug they might see as inconsequential. And that’s usually how it is with many companies/manufacturers, unfortunately. Even more successful ones like Nitecore and Lumintop that surely could refund/exchange more if they wanted to (although those two usually have more in the way of failures rather than design glitches, so to speak).
