[Python] AWS Lambda timing out on return statement

I'm trying to write a simple lambda function to use as a view for an application that has parquet data living in an S3 bucket. I'm just trying to test out a simple function here:

import json
import time
t = time.time()
print('This ')

import os
import urllib.parse
import boto3
import pandas as pd
import awswrangler as wr

print('Imports complete: ', time.time() - t)


s3 = boto3.client('s3')

def lambda_handler(event, context):
bucket = os.environ['S3_BUCKET']
try:
print('wrangling df')
df = wr.s3.read_parquet(bucket, dataset=True)
print('df loaded: ',time.time() - t)
response = df.to_json()
print('response type: ', type(response))
print('df to json: ',time.time() - t)
return response
except Exception as e:
print('exception caught: ',time.time() - t)
print(e)
print('Error getting object from bucket {}. Make sure they exist and your bucket is in the same region as this function.'.format(bucket))
raise e


I'm using the managed python layer on us-west-2:

arn:aws:lambda:eu-west-2:336392948345:layer:AWSSDKPandas-Python312:13


This is the output with a 60s timeout configured:

Test Event Name
(unsaved) test event

Response
{
"errorType": "Sandbox.Timedout",
"errorMessage": "RequestId: 24b0f94f-a78e-40e4-9573-0e49ac3eeef3 Error: Task timed out after 60.00 seconds"
}

Function Logs
This
Imports complete: 4.597054481506348
START RequestId: 24b0f94f-a78e-40e4-9573-0e49ac3eeef3 Version: $LATEST
wrangling df
df loaded: 10.094886779785156
response type: <class 'str'>
df to json: 10.67463231086731
END RequestId: 24b0f94f-a78e-40e4-9573-0e49ac3eeef3
REPORT RequestId: 24b0f94f-a78e-40e4-9573-0e49ac3eeef3 Duration: 60000.00 ms Billed Duration: 60000 ms Memory Size: 128 MB Max Memory Used: 126 MB Init Duration: 4874.63 ms Status: timeout

Request ID
24b0f94f-a78e-40e4-9573-0e49ac3


So it looks like the function is just hanging at the return statement when I test it. Oddly if I replace return response with return 'some text' it returns right after finishing. Why would a string several kbs long change the return time by 50+ s?

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