Getting duplicate AMI name client error, even though it is creating for the first time

Question

I am using a jenkins to trigger the lambda , which creates an AMI image from an ec2 instance, and then creates a launch configuration , and updates the auto scaling group with the new launch configuration , and let the auto scaling group creates the instances using the latest Launch configuration and terminates the older instances.

But my code some time runs properly but some time it give me "ClientError: An error occurred (InvalidAMIName.Duplicate) when calling the CreateImage operation: AMI name "API_AMI_200220_1629" is already in use by AMI ami-033a3681473f9acbd"

but my AMI names are dynamically created like "API_AMI_$(date +%d%m%y_%H%M)", so there will not be any duplicate AMIs that can be created technically. But I am getting this error and the AMI will be in a Pending state. can any one have any suggestion or a solution why it is happening only sometimes and not on all times.Please check the below codescript.

import json
import boto3
import time
def lambda_handler(event, context):
 flag_image=1
 instance_id=event['instanceId']
 ami_name=event['amiName']
 launch_config=event['launchConfig']
 autoscaling_name=event['autoscalingName']
 ec2_client = boto3.client('ec2',region_name='us-east-1')
 autoscaling_client = boto3.client('autoscaling',region_name='us-east-1')
 print ##############Creating Image########################
 response = ec2_client.create_image(InstanceId=instance_id, Name=ami_name)
 print response
 imageId=response['ImageId']
 print imageId
 describe_image = ec2_client.describe_images(ImageIds=[imageId])
 while flag_image == 1 :        
  for i in describe_image['Images']:
        time.sleep(5)
        print i['State']
        if i['State'] == 'available':
             flag_image=0
        describe_image = ec2_client.describe_images(ImageIds=[imageId])

Thanks in advance.