Problem with unwanted blinking LEDs - ESP32 project

[Skotee]

Hello,

I want to make Tetris game, based on LED's matrix 16x9 with WS2812B leds and ESP32 DevKit.
Already, project is almost ready from hardware side (soldering and housing).
Before coding the proper game I wanted to test BT connection with my app made with Thunkable. After connecting matrix with app by BT, and clicking button responsible for running animations from strandtest (example how it looks: https://www.youtube.com/watch?v=X1mfjO-0dX0) the strandtest is running, but LED's are blinking randomly.
Maybe someone here knows, what is happening and how to fix this?

Strandtest without app: https://drive.google.com/open?id=1UWROc ... yqOkVTX_rU
Strandtest runned with app and BT connection (and unwanted blinking): https://drive.google.com/open?id=1eA5cZ ... IcRIud_S99

To configure test I was using this tutorial: https://www.instructables.com/id/ESP32- ... E-AWESOME/
In main.cpp I've pasted piece of strandtest code.