It sounds like LED driver U4 is not operating correctly. Try swapping the two LED driver chips (U4 and U5).
If the problem changes (for example, if none of the LEDs light), then that driver chip will need to be replaced.
If the situation does not change, then the chip is most likely fine, but there is something about how it is wired or soldered that is causing the problem. Carefully check to see if there are any short circuits — accidental connections — on the pins below it, or possibly under the socket on the top side. Check to make sure that there are not any poor, dry, or incomplete solder joints on that socket. Make sure that the chip is firmly seated in the socket as well.