Why is amplify saving username incorrectly? - reactjs

Question

I have a function to create a vehicle in my amplify project:
const createNewVehicle = async () => {
const { year, make, model, vinNumber } = searchedVehicleInfo || {};
try {
await API.graphql({
query: createVehicle,
variables: { input: { year, make, model, vinNumber } },
authMode: 'AMAZON_COGNITO_USER_POOLS',
});
} catch (err) {
console.log(err);
return null;
}
};
This function creates a vehicle in my dynamoDB table utilizing the API module exposed by amplify. The authMode property saves the Cognito user's username in the API request as well. The vehicle's graphql model looks like this:
type Vehicle
#model
#auth(
rules: [
{
allow: owner
ownerField: "username"
operations: [create, read, update, delete]
}
{ allow: public, operations: [read] }
]
) {
id: ID!
year: Int!
make: String!
model: String!
vinNumber: String!
image: String
username: String
#index(name: "vehiclesByUsername", queryField: "vehiclesByUsername")
receipts: [Receipt] #hasMany(indexName: "byVehicle", fields: ["id"])
}
A team member created his own AWS account and set up his own environment to be used in amplify. This team member created an IAM user and applied the AdminAccess-Amplify role to his user. When he uses this function, the vehicle is created, but it saves the username in a weird way. If his username is test12 it will save the vehicle with a username like this 6e0b3347-5dae-4106-aed6-8ec5c87fde52::test12. So when I try to grab vehicles by username, none come up because his username is test12 and not 6e0b3347-5dae-4106-aed6-8ec5c87fde52::test12.
How can I get it to save just the username and not all the extra information?