It was a mistake on my part that didn't pay attention to the tree too much. I have 1 of my colonist prune 2 of the Gaulanren trees.
after a long await, the forth dryad is spawn. The mistake was that the connection strength of that tree was exactly 75 and the said colonist is sleeping. After half an hour in game time, the new born dyad just disappear immediately.
I have my pruner rush to his overtime job but the tree said the next spawn is next 8 days >:( !
Wish they should wandering around just 1-2 days when the connection power is below the threshold, not just disappear like that.
sorry for the rant.