I have an S2+ with the following problem. The light has 5 modes. When turning it on, it always comes on in the next mode from when you turned it off. I normally run it on high. When I turn it on it comes on in strobe (which is the one after high.)
Any idea? This one only has about 1n hour of use.
Thanks
Wow, next mode memory when it's not supposed to be...
That sucks.
I hope someone smarter than me can help you out! 
It should remember your last mode if you had it in that mode for at least 3 seconds. If you have it on or in a certain mode for less than 3 seconds, it won’t work. I’m not sure if that’s your problem, but I had some confusion with a light with a similar Memory function when I first got it and was just testing it out.
Maybe the switch or driver retaining rings are loose causing a simulated double click when you turn it on —- try taking off the tail cap and using a screwdiver or something to turn the light on and then off —then turn it back on again and see what happens
My mom has a flashlight that she has dropped one too many times.
It was the typical five mode, but with proper memory.
Now it's one mode--high or off.
I told her, "I don't know how to fix flashlights, so it's just a one mode flashlight now." 
(She actually doesn't mind so much because she usually used it on high.)
If it is the older 3/5 mode UI then there is a 3 second mode memory timer i.e. a mode is only memorised when it has been on for more than 3 seconds.
This ^^^^^^^^^
The trick is to be patient and wait the 3 seconds.
I am talking about turning it on after not using it for a day or a week.
It is not a matter of how long it is turned off before you use it again.
The question is how long it was on, before it was turned off.
Walking with your light on high all the time, then turn it off, the light will restart in high.
A lot of people (unconsciously) fiddle before turning it of. Then it restarts at the next level of whatever mode you turned it off
To be clear, even if I have it on for an hour, when I turn it off then on it goes into the next mode .This happens regardless of how long I have it off or on and regardless of what mode its in. It will start on the next mode 90% of the time. 10% of the time , it works fine.
Not heard of this issue on those lights before. Switch bouncing? When you turn it on, see if you can click it a little differently? I don’t think you can with those clicky switches. Otherwise test without the switch by removing tail-cap and short battery minus with the tube. If you still have the issue when doing this, then switch bounce isn’t the issue.
It could be the 3 second bit, since i got my first light i trained myself to use a mode at least a few seconds except when i want to skip modes intentionally to get to the one i want.
That said i would not want a procedure for just one light so the tap just this light 4 times would not work for me. A few secs on all lights i own works fine becasue its uniform.
While this is a good solution i would be curious to see a teardown to determine what caused this to happen.
Have you tried what is mentioned above???