In the Invasion scenario, I noticed that some events have a lightning bolt icon. I assumed this meant that the event is actually resolved at the start of the round, but I did not see this mentioned in the rules.
It's covered on page 6 of the rulebook. White box, bottom of the page.
Note: Event Tiles with a 'lightning bolt' symbol are extra mean. If you do not like that, sort those out before preparing the Event Stack. If you want a greater challenge, leave all Events in the game and instead sort out “Support” and “Training”.