https://www.gamespot.com/articles/theres-a-rainbow-six-patriots-easter-egg-in-ghost-/1100-6460505/

Following the Splinter Cell missions with Sam Fisher, Ghost Recon: Wildlands is crossing over with yet another Tom Clancy franchise: Rainbow Six. We already spent several hours with the update, and toward the end of the content we discovered a tongue-in-cheek reference to Rainbow Six: Patriots, one of Ubisoft's notorious cancelled projects.

In addition to a new permadeath difficulty and updates to its PvP mode, Wildlands' newest DLC brings several characters from Rainbow Six Siege to open-world Bolivia.