Just to add to what meganoth said, the game saves different data at different intervals based on how important the data is so you don't have pauses while saving everything at once. If a game is improperly shut down in some way or there is some issue saving, the position of your vehicles can be a past location (usually within just a few minutes). Backtracking your path will usually allow you to find the vehicle. Sometimes the vehicle won't show on the compass in such situations until you are very close to it. Using the console is a good way to find it, but I know that's limited on consoles, so I'm not sure how good that will be for you. If the console shows the recent section of a log file like it does on PC, you can also look in that shortly after loading the game and you should see the vehicle locations listed and can then go to the location that way.