Weird signal issues when using bigger amount of RGBW LEDs

Hello, I am trying to control ~50 LEDs in a RGBW LED strip. It works fine when I use 5-10 LEDs, but when I try to use 50, it does behave in quite weird way. The way it behaves in is similar as before, when I was controling 5 LEDs without logic level converter. It tries to do what I want - light one LED up in sequential order in blue, but other colors are randomly flashing and I have no clue what could cause this. I dont have osciloscope to check the data line, but I think the data line might be the issue, any ideas on how to debug this?

Im using rpi_ws281x library on Raspberry Pi 3 B, LEDs are powered using external 5v source

This is normal if you don't use a level converter. 3,3volt can work for short distances but 3,3 volt is outside the specification for WS28XX LEDs.

I am using level converter. I've now soldered the setup into a prototype PCB board and it is working like a charm. I think my issue was that I was powering the level converter HV part using RPI's 5V pin, however I was supplying voltage to the pin using external power source. Thanks for the input, though!

Weird issue, glad you find out what the issue was.