^^^^
on a switching constant current driver without load(the switch is off*) the voltage rise up to the maximum, the stored energie in the
capacitor at the output stage is now also on its highest point.
if you now reconnect the leds, this high voltage drive a high current through the leds for a short moment, and now it depends on how much leds are in the string. shorter strings(number of leds in series) have a higher killrate.
13 Leds on a
Meanwell LPC 35-700 in this situation...
the leds here are good to 1 Amps with peaks up to 2 Amps(10 msek).
one dead, one short, and a third one starts blinking after some minutes, strange thermal effect on this one.
https://www.rollitup.org/led-other-lighting/547085-diy-modular-led-light.html#post7754589
all above is only correct for switching constant current drivers.
*assumption> the switch is between driver and leds