LED matrix - after sometime LED's started flickering or not repeating /loop

Hello, please help for below Arduino code issue, it is running for sometime(patterns are working fine) then started flickering or blink for sometime , it is not looping/repeating .

this is 12 X 12 LED Neopixel, this is not my code, am just started using Arduino programming. please help to understand what causing this issue.

thanks

12x12_matrix.ino (32 KB)