Buck Converter and WS2812 LEDs
Sorry, you cannot wire two standard buck converters in parallel. They are not designed to share current. Try separating the LEDs into sets where the number of LEDs in each set does not exceed 2A. The GND and control signals can be wired together but not the power.

Why?  Each buck converter is trying to achieve an output voltage of 5.000V. Due to component tolerances, the actual voltage produced by each buck converter will vary perhaps by tens of millivolts or more. If the two voltages are not exactly the same (and they won't be) they will fight each other.

If you absolutely, positively need to parallel the buck converters, you can try droop sharing. Droop sharing requires careful calibration of the module output voltage and you have to waste some power with series resistance and the current sharing may not be great, but it might be an option for you.

Checkout page 5 of this document. 

But... it's better and simpler to separate the LEDs into sets that can be independently powered.