Rockstar has advised players to avoid using GTA 5's garages while it investigates a fix for disappearing vehicles and upgrades.
In an update on its support site, Rockstar acknowledged the bug saying that the issue "may occur if you drive another character's personal vehicle" and that it is "looking into a fix to prevent this from occurring in the future".
"In the meantime, please try to avoid parking a car in a garage, driving one already in a garage, or getting in a default vehicle, when playing as a character other than the one with your upgrades."
The garage is supposed to store the player's vehicles and upgrades, but many players have reported losing their vehicles after storing them - including those with extensive customisations.
GTA 5 launched last Tuesday to become the fastest-selling entertainment property in history, generating over $1 billion worth of revenue within its first three days on sale.