There are two types of pop-ups… The type that pop-up when you are stopped and show things around your area…
When driving (doesn’t matter if you are in navigation mode or not, but navigation mode helps predict these better) you’ll get a pop-up when you approach then (i.e. “Watch Out, Police reported Ahead” with a popup with two buttons, “Not There” and “Thanks”)
You can also get pop ups while on the move if the report was sent by another wazer in the same main waze group as you are or on other groups you follow. This can be set in the client options.
The popup notification being discussed, happens when the hazard/police is on your side of the road and on the road you are (or will be) driving on and pops up while driving with the “Not There” and “Thanks” button. This is not the same as the rotating popups which appear when stopped.