Hi there.
1. I think that’s because your bath particular is too low. So when you wanna make the particulars hav a longer life. On this time point the number of particulars are reach the limit. They can’t bath new particulars on this time unless in this time point there are some particulars were died.
2. If you wanna this flowers randomly dispirited. You can try the Luma texture. Give the texture a ramp to control the direction,speed. Also you can give the texture the noise effect. Put the channel on Luma.
Hope that’s can help you. And I really wanna know how do you creat the flower animation on AE soft?
https://videohive.net/user/untruelife