My Convoy S2 was flickering, and after well over 1000 hours of use (maybe over 2000) it does not owe me much, but a quick clean of the metal current conducting surfaces in the body and tailcap its working fine again.
How is the reliability of your lights, stock and modded?
My Keygos KE-5 now sometimes won't come on for reasons I know not.
none of mine but ive had some friends flashlights fail. both were ultrafire 501B hosts with some work done to them by me. neither failures were because of them being 501B’s 
one was the LED got knocked off cause the owner kept dropping it many, many times.
I replaced the LED with a neutral white xm-l t6. rather than using the heatsink glue, i used arctic silver paste… so when he drops it again, the mcpcb can slide some just in case that was the issue.
the other was a MCU getting knocked half off the driver board. again, dropping being the culprit. upon dropping, the battery slammed into the driver board and flexed the board enough that the MCU pads cracked and the chip would disconnect itself.
new driver. problem solved.
I handle my own lights with kid gloves. no failures here.
Brian
K40 & TN31 resistors bridged: Had the battery holder springs go too hot and lose their tension and just collapse. Fixed with copper braiding.
Convoy S8: Working just fine even with a dedome.
BLF X6 SE: A few weeks of ownership but seems great except for the PWM whine.
Nitecore P10 with slightly switch button issue, not the strobe ready/mode switch but the main switch, 10% of all time it will not turn on when fully pressed down for locked/constant on, not a big issue but a bit bothering.
I had a XinTD X3 switch fail, but that’s about it.
I bought a "fair amount of lights" so I would not consider myself unlucky despite that the following fails..
Budget lights
-UF1405, switch issue, did not work all the time
-Fandyfire Warrior, one of the E-switches had an issue, did not work all the time
-UF-T20, bought multiple since a local wanted lots of them modified. Several switch issues upon a arrival so I swapped switches in all lights.
Probably some more switch issues that I cant remember too. Most of these are easy to fix and not unusual issues on cheap lights. How many other things I have fixed or improved Im not able to keep track off. Lots of small stuff that could have lead to failures.
Premium lights
-Supbeam K50 - It can be discussed if the battery carrier got damaged due to a mod attempt or just a/the design fault. Either way, the electronics saw too much heat. The light still worked, but components inside the battery carrier did not look good. Even stock carriers can heat up to levels that I would not consider healthy. Most people will not know or notice though. But even on a bone stock light, these can heat up too much when used on highest turbo output with the right low voltage cells.
-Supbeam X60 - Periodically accidental strobe activation when used on high. Im pretty sure the reason behind this "fail" is because of the magnetic field for strobe is too close to the highest output setting. Margin of error/magnetic field seems too small.
Modified lights
-I had a de-domed XP-G2 fail in a UF-T20 that I modified last year. :_( First real fail in any light I have modified. Im not sure why the de-domed emitter failed. Never had that happen before and it had been working for a long time. Im a bit more careful with the de-domed emitters these days though. I also had a wire come off spring from a spring mod in another light.
Normally lights that I modify gets increased reliability. Potential faults and issues gets taken care of. Although, on a few lights I just use stock drivers pushed beyond the limits and cross my fingers. Example, stock UF1405 driver with over 250% increase in output. Im not going to claim increased driver reliability. :p I would not be that surprised if it failed in the long run despite surviving some reliability testing. But thanks to some fixes the light is now more reliable then when it was stock. I know which of my lights that might be living on the edge.
All issues/fails mentioned above are/were fixable though. Most quick, simple and super cheap fixes. Except the K50 issue, but that may not be considered a fail. I just don't like the issue. Not acceptable considering the price of the light.
My X3 also failed.
I had a few of the lower price budget lights fail…attempting to put new drivers in them. I really hate having flashlights not working (I still have to build my color light C_K gifted to me as well)
TN32. No help at all from the manufacturer.
I had my first light failure today. Not only that, but I may have had two failures. :zipper_mouth_face:
First one was a CNQ SS AA that I used a 14500 on when it could only handle AA. Second one was an Olight ST25 that I leave in the shower area - so much for that IPX-8 (waterproof to 2m) rating… The light was never even submerged… I might be able to get the Olight to work by drying it out, but the CNQ is definitely burnt out.
probably 2 of my sipik sk68 modded with osram emitter
worked awesome with no flaws
woke up one day and the osram led just died
no current can pass through. just a broken circuit in the led
MRsDNF can i ask what issue you have? I have only seen one reported issue and that was the led fried [ gday Roberto] and was replaced under warranty-
There was a dry solder on the driver causing the light to not operate. I did mention it on here somewhere awhile ago. I had no response from them at all.
My starry light is dying, the threads are wearing out so soon i won’t be able to screw the head onto the body, its a good light, but with a fatal design flaw 
Just thinking out aloud here but would Teflon tape help here?
Good idea, i thought of electrical tape tape but figured it was too thick, for the life of me i did not envision tape of the teflon variety, even though i have several rolls of it.
You have just prolonged the lifetime of my light 
My stocks sk68 clones all died pretty fast on me. And they were not even used regularly!