The reason is because line 2.
I had limited the number to 20 instead of 140.

Thanks,
Frank

I would also like to add that some LEDs that come well after the 19th LED still light up with the color and from the previous project. I also find that remarkable.

I have an ESP32, a BTF-LIGHTING WS2812B 5M LED light strip and a 5V 10A RS-50-50 power supply unit.
I connect it like this:
https://mehlhop.com/forum/ESP32-plan.png

And I add this program:
#include <FastLED.h>
#define NUM_LEDS 20
#define DATA_PIN 2
CRGB leds[NUM_LEDS];
void setup()
{
FastLED ...