right click on the games icon in origin and repair the install. it will just check the files and repair any that are broken.
also if you get the bug where your hands are gone as well then press 1 or 2 on the keyboard this will cause the game to stutter but your weapon should appear but with a slight jerk on the gfx. most times a pistol. hit weapon swap again and the correct weapon will appear at normal speed.
problem is that this was a known bug at release and was fixed. so my guess is your files need updating.