Multiple file upload does not work

**Bug description**
I have a mutation which includes 4 complex S3ObjectInput but when I call it AppSync client uploads only first one.
```graphql
mutation SendRideData(
$id: String!,
$workoutName: String!,
$email: AWSEmail!,
$duration: Int!,
$powerAvg: Int!,
$powerMax: Int!,
$rpmAvg: Int!,
$rpmMax: Int!,
$hrAvg: Int!,
$hrMax: Int!,
$json: S3ObjectInput,
$tcx: S3ObjectInput,
$imageRPM: S3ObjectInput,
$imageHR: S3ObjectInput,
$imagePower: S3ObjectInput) {
rideDataEmail(input: {
id: $id
workoutName: $workoutName
email: $email
duration: $duration
powerAvg: $powerAvg
powerMax: $powerMax
rpmAvg: $rpmAvg
rpmMax: $rpmMax
hrAvg: $hrAvg
hrMax: $hrMax
tcx: $tcx
imageRPM: $imageRPM
imageHR: $imageHR
json: $json
imagePower: $imagePower
}) {
workoutName
email
json {
bucket
key
region
}
}
}
```
**Expected behavior**
To upload all of the S3ObjectInput objects

**Environment(please complete the following information):**
- AppSync SDK Version: 2.7.9
- S3 SDK Version: 2.13.5