LED Fault in PCB - Some strings of LEDs intermittently dim
Sometimes, when the LEDs are dimmed, pressing down on the board causes them to light up properly.


This would seem to indicate that you have intermittent connections in the circuit.
It's certainly possible that tracks may be damaged, but it seems more likely the problem is cracked resistors or stressed solder joints on your components. 

Check the soldering quality and you might be able to find broken resistors and component connections with either a cold spray or heat gun.