1. The LED lamp bead or resistance may be damaged.
2. It may be component virtual welding or de-welding.
3, may be what you said, the led pcb board is not good, can be used to detect the multimeter between the components of the line, whether disconnected.
In order to have a good heat dissipation effect, LED pcb board is usually aluminum substrate, the first layer is the surface line, the second layer is the insulation layer, the third layer is aluminum plate.