from the announcement:
This time around, at the start of the event we’ll also be releasing a brand new line of Gleam Storage items in Plain, Stylish and Ornate variants for you to keep all your shiny new Gleambow rewards in. These will still be available to be crafted after the event ends. New for this version of the event, Gleambow Meteorites may now also be made of Glass, and we’re going to be adding two awesome new cosmetics to the Exchange to go along with the ever-popular Gleamicorn Horn from last time.
So I guess it’s when they released the gleam closed storage as well as a couple of new wearables. No substantial rule change but I think it was during the second event when they tried some new timer settings, and times for the meteors were getting as long as 15 minutes or something crazy.
After that it was REALLY hard to go back to the usual settings 
EDIT: for fun here’s the most screenshots I ever tried to post in a forum thread:
During the event I had tried to get a shot of every dormant meteor I came across.
EDIT2: lol ok enough rabbit holing!!!
