I was experiencing this issue too.
At the beginning I received 2-4 bolts from EVERY 8-hours harvesting (from 6 farms)
But then I planted eliteleeks for a few days, it is about ten harvests total - and got ZERO. You think it is correct drop?!
Then I started plant 20-h crops and receive bolts, right, but there was still no bolts from eliteleeks and diamondates (these two!). So I still think it was a bug!
But support says that it is just unluck and no bug at all.
I think it is not correct situation - I received bolts properly, then - bam! - a ZERO for a few days. Even it is a chance and so on...
What I have to do to get the dragons? Where I have to write if I think that support is wrong?