What triggers the change of music on the Avenger?
In XCOM 2 (and XCOM 1 as well), the story follows a Three Act formula denoted by a different music track playing during each act while on The Avenger. The tracks in XCOM 2 are titled Stage One, Lazarus (for the second stage), and Stage Three. However, as the differences between the tracks are relatively subtle, it can be difficult to notice exactly when they change.
What events trigger the switch between acts, and consequently, between music tracks?