Greengrass MQTT (Moquette) Broker throwing max size allowed error on UpdateThingShadowRequest with 10KB payload

We are running version 2.3.5 and I have verified the max size is 128KB in the broker config:

componentType: "PLUGIN"
configuration:
  moquette:
    host: "0.0.0.0"
    netty.mqtt.message_size: "131072"
    ssl_port: "8883"
  netty.channel.read.limit: 524288
  netty.channel.write.limit: 524288
  startupTimeoutSeconds: "120"
dependencies:
- "aws.greengrass.clientdevices.Auth:HARD"
lifecycle:
  startup:
    timeout: "120"
version: "2.3.5"

Here is the python code calling the shadow update:

update_thing_shadow_request = UpdateThingShadowRequest()
update_thing_shadow_request.thing_name = self.thing_name
update_thing_shadow_request.shadow_name = ''  # Default shadow
update_thing_shadow_request.payload = payload

op = self.publish_ipc_client.new_update_thing_shadow()
op.activate(update_thing_shadow_request)
fut = op.get_response()
result = fut.result(TIMEOUT)

My payload size is well under the maximum allowed:

>>> getsizeof(payload)
10998

However, I get the following error when sending this payload: {"message":"The payload exceeds the maximum size allowed","_service":"aws.greengrass#GreengrassCoreIPC","_message":"The payload exceeds the maximum size allowed","_errorCode":"InvalidArgumentsError"}''}

Is there another setting that I am missing?