For everyone that is struggling with fixing the ambilight random flickering and the ambilight is made with ws2812b + Raspberry Pi + Arduino there is a few things that each separate one (or any combination of them) can fix the issue. I was struggling few months too. Tried every suggestion on the web (software and hardware), missing one thing that wasn't suggested anywhere. It was not included in any tutorial too. The fix in my case was connecting one of the ground pins of the Raspberry to the grounds of the Arduino and the strip (all of them grounded in the power supply V-). There wasn't any tutorial that was saying that they (3 of them) must have common ground. All suggestions were that I have to have common grounds on the arduino and the LED strip.
So, this is short list of things that may help:
- putting additional capacitor 1800uF 6V+ (and more) on the power supply V+ and V-
- putting resistor 470 Ohm directly or as much closer as it can be placed on the first LED DI (Data In) connector
- using short and thick wires to power the LED Strip to prevent voltage drop and supply enough amps for the LED Strip
- If the strip is longer (let say 150, 200 or 300 leds and more) power it on a few places along its length and even on the end. Measure the voltage in between 2 power connections to check if additional power connection is needed to fix the voltage drop.
- Calculate the Amps needed to feed the strip. Each LED consumes 60mA. When buying the power supply and choosing the right one for you, use this formula to calculate how much power in watts do you need: P(W) = I(A) × V(V). So lets say 300 LED multiplied by 60mA = 18 000mA = 18A. 18A multiplied by 5V = 90W - needed only for the strip! But hey, don't be scrumpy when buying power supply - buy 100W. And read the buyer comments under the product and make sure if it is good quality. You don't want to fire you house or damage electronics for hundred dollars, right?
- When testing the configuration is done and everything works amazing, don't forget to use good quality and more thicker cables. Avoid any use of solderless power, ground and data joints. It may lead to power and voltage drops, loose/no connection at all and we know that with the bigger power comes bigger responsibility 
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