Program is not working consistantly

Projects General Guidance
1

Hello, hope you can help to solve the issue,

I wonder what causes the program is not working consistently. I worked on SPI camera, but sometimes it runs and sometimes it doesn't. Even I used the Teensy 3.6 board or Leonardo board and it happens the same. I also changed the camera but it still the issue. Any advice?

Thanks

2

Add debug output to your code, to learn more about where the program hangs.

3

I'm not sure how "Add debug output to the code". would you teach me how? Thanks

4

Add some print commands at strategic points to print out some variable values, blink an led