New to Arduino and LEDs and trying to pick it up, but I’m not sure where I am going wrong. I have been hacking at the example sketches trying to figure them out but noticed some strange behavior from the LEDs. So I backed it up to the very basic one from the FastLED GitHub blinking the first LED. Although this does rapidly flash the first LED white randomly other LEDs will also flash various colors. It is almost like there is a memory of prior sketches that is not being overwritten. My setup is an Arduino Uno and an Adafruit 1m (30 LED) WS2812B strip (same issue when working with a 5m strip of WS2811). LEDs are powered by 3 AA battery pack with a capacitor in between, Arduino from USB.
in addition to the data line connecting to the arduino to the leds, do you also have ground connected between the arduino and the leds? Without that all sorts of weird stuff will happen 