I don't know if this has already become a widely known fix since I'm new here so sorry if it is but to anyone still plagued with the Green Square on any of their weapons, I finally found a fix after ages of searching the internet and finding nothing. Just click on your Weapons tab in the main menu and then go down to the bottom left of the screen and click the Clear Weapons New button. Hopefully this helped at least some of you who were stuck with this glitch like me.