Fixes uploaded to sort completedParts before completing the upload

backend/media/uploader.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"sort"
 	"sync"
 
 	"github.com/aws/aws-sdk-go-v2/aws"
@@ -187,6 +188,11 @@ outer:
 		uploadedBytes += result.size
 	}
 
+	// the parts may be out of order, especially with slow network conditions:
+	sort.Slice(completedParts, func(i, j int) bool {
+		return completedParts[i].PartNumber < completedParts[j].PartNumber
+	})
+
 	completeInput := s3.CompleteMultipartUploadInput{
 		Bucket:          aws.String(bucket),
 		Key:             aws.String(key),