When the wall of photos of missing people is shown, the same photos are used over and over in different ways.
When Feinberg and Wolf are discussing matters after the opera (~1:21:00), Gustav Holst's Mars movement from his Planets symphony can be heard very low in the background. This piece is often associated to a conflict negotiation between two major characters, and can arguably be heard as inspiration for the Darth Vader theme in Star Wars: Episode IV - A New Hope (1977).
Charles Wolf (Stanley Tucci) gives advice to another character by telling a story from his past life about a bridge. Tucci did a very similar scene in Margin Call (2011), where his character (Eric Dale) also gives someone advice by recounting a story about a bridge in his past life.
Michael Keaton and Stanley Tucci previously worked on Spotlight (2015), although they didn't share any scenes together.
Michael Keaton and Amy Ryan previously worked together on Birdman or (The Unexpected Virtue of Ignorance) (2014).