improper lapis ore generation

In this version, there are fewer lapis ores than diamond ores. Is this a problem or a spec?

 

The followings are what I tried.

  I tried branch mining to use up 8 iron pickels, but no lapis was found.

 I blow up TNTs but I found less lapis ores than diamond ores.

 

I'm sorry but I'm not good at English :'(