The cause of Brett Gardner's son's sudden death remains a mystery ... but Costa Rican officials said Tuesday they believe food poisoning might have played a role in the tragedy.
14-year-old Miller Gardner passed away Friday while on vacation with Brett and other family members in Manual Antonio ... and, initially, investigators thought he might have died from asphyxia, as his body was found with vomit on it.
But Costa Rica's Judicial Investigation Police told CNN on Tuesday that after they discovered the teen's airways were clear, they now believe his body's unfortunate reaction to a meal was what sparked the passing.