Why is the transition stopping?

Question

I'm using DOM and CSS transition to make a rainfall effect, only the droplets are disappearing halfway.
https://code.sololearn.com/WZl6y6ZhZaZU/?ref=app

Answer 1

Because every time a new drop spawns, the transition will reset

Answer 2

https://code.sololearn.com/Wpwp68mgsCDZ/?ref=app
I just changed the setInterval.Its stop half way because your cas time is 2s and the others is 5millisecond.