Arduino Mega PWM conflicts?

Hello, I am in progress of doing an aquarium controller with multiple inputs and outputs. I got stuck, and I need little bit of guidance to trouble shoot my project.

Short description of the hardware: - Mega 2560 R3 - Ethernet + MicroSD shield (MOSI and PWM pins 4 and 10 are used for SS). - RTC 1307 (SDA, SCL) - pH shield connected to Serial 2 (RX/TX). - IR remote on pin 32 - LCD on pins 22 to 37 - 2x DSB1820 on pin 2 (PWM) - most of the other pins are going to be used by sensors or relays, basic 0 or 1 state.

For controlling the lights I opted for PWM, pins 5, 6, 7, 8, 11, 12, and 13. Each channel can take values from 0 to 255

int Act1_pin = 5;
int DL1_pin = 6;
int UV1_pin = 7;
int Act2_pin = 8;
int DL2_pin = 11;
int UV2_pin = 12;
int ML_pin = 13;

The issue that I am having is with Pin 12 PWM. Instead of keeping solid ON (at 255), it starts flickering (randomly). It looks that I have a conflict with some hardware and/or libraries that I am using. At this point I ran out of my troubleshooting possibilities. In setup section I added a testing procedure, so everything is fine at this point. Example:

  analogWrite(DL2_pin, 255);   delay(100);
  analogWrite(UV2_pin, 255);   delay(100);
  analogWrite(ML_pin, 255);   delay(100);

  analogWrite(DL2_pin, 0);   delay(10);
  analogWrite(UV2_pin, 0);   delay(10);
  analogWrite(ML_pin, 0);   delay(10);

I change the output value with simple analogwrite in IF statements and everything works fine for the other channels.

if (UVLightMode==1){UVOutputValue = UVOutputValue + 1; analogWrite(UV1_pin, UVOutputValue); analogWrite(UV2_pin, UVOutputValue);}

I stayed away from PWM pins 4 and 10 that are used by the Ethernet/SD shield. Wondering if you folks see other known conflicts with this kind of hardware? What is using PIN 12? Are the other PWM pins getting in conflict with #12? I do not know what else to share. Please help.

Found the issue :). One defective LED used for control. :0 I spent so many hours looking for PWM conflicts, timer pairs, libraries, etc.