So it was something about the leds that they only worked above a certain brightness level? They just turned off as the brightness got too low? That is very strange.
Maybe one of the leds was defective causing them all to behave the same?
I don’t have experience with that situation, sorry.
I never heard of LED's behaving like this either, but who knows, could be possible. I've done a lot of MCPCB mods including grinding them down and never had problems.