Have my LEDs failed over time?
You may have damaged LEDs. Do not connect LED in parallel. They are not exactly equal. Two separate resistors for each row value 12 Ohm 2W should be.Due to some inequality in LED one row may have current bigger than another. It will damage LEDs. After they gone and not conduct current second row is damaged because of excessive current. And that kind of diodes require heatsink, that small PCBs not enough to dissipate heat