The LG G4 was released in the US in early June 2015, as always focusing on high-end specifications and a refined fashion sense that makes it stand out in the premium smartphone market. Each version of the phone will have a different model number based on if it is sold by a carrier or unlocked (US or International). Some LG G4's are known to have bootloop problems.
Are your apps actually deleted or just moved off the home page . Can you go into the apps and find it there. If its in the apps storage than you wont be able to reinstall it as its already there.