adam

Could be a bad/insufficient/old power supply, bad/counterfeit/mis-inserted SD card, bad/wrong/corrupted image, .... you really should view the serial console[1] to see if there's any useful message or any legible output at all.  If you must fly blind, first try rewriting the SD card, making sure you're using the correct stable image for the board and verifying that it was downloaded, extracted, and written to the card properly.
 
[1] See http://lucsmall.com/2017/01/19/beginners-guide-to-the-orange-pi-zero/ (read the note on the USB-to-serial converter voltage level before the "Software requirements" heading, then skip to "Alternative strategy, using USB-to-serial converter")

Devs are fiddling daily in the code, there is some code sanity checks and script just build everything + builds around 30 testing images, starting at 0:00 and finishes at around 8am. In the morning we see whether it builds fine or breaks building, but we don't know if all boards boots until somebody do the actual boot. When the problems is find, fix goes to the source and everything repeats the next day ...

Once again. You can use nightly builds, while you don't have rights to complain if something doesn't work  Usually many things doesn't work, regressions happens and we are aware of that. Explaining this again and again is counterproductive. 
 
Edit: fixed today

Maybe switching from 'Nightly' (experimental/unsupported) to normal images?