If you find your avatar not being displayed correctly for any reason, go to the Looks section of your Profile. Find the missing body part and re-select the part that's causing problems. You'll see the entry for the missing part will be blank (it should never be blank). That will fix this sort of problem.
If you are having any other sort of avatar display problem, try making a small visible change to any part of your avatar, (change eyebrow color, for example) and that will cause your entire avatar to be redrawn, likely fixing the display problem.