Whilst using FSX today, During boarding I noticed that the arriving baggage tractor, it's body was transparent except for the wheels and a few minor details (refer attachment #1).
Doesn't happen here, it must a problem of your graphic settings.
Furthermore whilst in the push back phase I also noticed the 'wing walker' to be invisible except for a shadow of himself (refer attachmnet #2).
Doesn't happen here either, it must a problem of your graphic settings.
Try to reset if your FSX.CFG file to default, by removing the FSX.CFG located at %APPDATA%\Microsoft\FSX, this will force FSX to rebuild a new one with default setting. You likely have a wrong tweak set.