MicroROS: RTPS error

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Hi, I'm running a MicroROS publisher on a Portenta H7, and I'm using a custom message type of the format:

EIClassification.msg
---
string label
float32 value

And it was working just fine for me: I was able to echo the MicroROS topic with no problem. I must have somehow changed some parameter somewhere because now when I try to echo the topic I am seeing:

2022-09-13 20:48:29.787 [RTPS_READER_HISTORY Error] Change payload size of '24' bytes is larger than the history payload size of '11' bytes and cannot be resized. -> Function can_change_be_added_nts

This runs repeatedly, seemingly upon every publish.

I would greatly appreciate any ideas as to where to look... I tried digging through whatever RTPS-related files I could find in /opt/ros but didn't see anything obvious.

Arduino code:

#include <micro_ros_arduino.h>

#include <stdio.h>
#include <rcl/rcl.h>
#include <rcl/error_handling.h>
#include <rclc/rclc.h>
#include <rclc/executor.h>

#include <ei_interfaces/msg/ei_classification.h>

rcl_publisher_t publisher;
rclc_executor_t executor;
rclc_support_t support;
rcl_allocator_t allocator;
rcl_node_t node;
rcl_timer_t timer;

ei_interfaces__msg__EIClassification msg;

#define LED_PIN 13

#define RCCHECK(fn) { rcl_ret_t temp_rc = fn; if((temp_rc != RCL_RET_OK)){error_loop();}}
#define RCSOFTCHECK(fn) { rcl_ret_t temp_rc = fn; if((temp_rc != RCL_RET_OK)){}}


void error_loop(){
  while(1){
    digitalWrite(LED_PIN, !digitalRead(LED_PIN));
    delay(100);
  }
}

void timer_callback(rcl_timer_t * timer, int64_t last_call_time)
{  
  RCLC_UNUSED(last_call_time);
    if (timer != NULL) {
    RCSOFTCHECK(rcl_publish(&publisher, &msg, NULL));
  }
}

void setup() {
  set_microros_transports();

  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, HIGH);  

  delay(1000);

  allocator = rcl_get_default_allocator();

  //create init_options
  RCCHECK(rclc_support_init(&support, 0, NULL, &allocator));

  // create node
  RCCHECK(rclc_node_init_default(&node, "micro_ros_arduino_node", "", &support));

  // create publisher
  RCCHECK(rclc_publisher_init_default(
    &publisher,
    &node,
    ROSIDL_GET_MSG_TYPE_SUPPORT(ei_interfaces, msg, EIClassification),
    "/micro_ros_arduino_node_publisher"));

  // create timer,
  const unsigned int timer_timeout = 200;
  RCCHECK(rclc_timer_init_default(
    &timer,
    &support,
    RCL_MS_TO_NS(timer_timeout),
    timer_callback));

  // create executor
  RCCHECK(rclc_executor_init(&executor, &support.context, 1, &allocator));
  RCCHECK(rclc_executor_add_timer(&executor, &timer));

  // Fill the 'label' array with a known sequence
  msg.label.data = (char * ) malloc(25 * sizeof(char));
  msg.label.size = 0;
  msg.label.capacity = 25;

  strcpy(msg.label.data, "test_label");
  msg.label.size = strlen(msg.label.data);
  msg.value = 0.5;
}

void loop() {
  delay(50);
  RCSOFTCHECK(rclc_executor_spin_some(&executor, RCL_MS_TO_NS(100)));
}

Output from MicroROS agent (docker):

...
[1663092212.433801] debug    | DataWriter.cpp     | write                    | [** <<DDS>> **]        | client_key: 0x00000000, len: 20, data: 
0000: 0B 00 00 00 74 65 73 74 5F 6C 61 62 65 6C 00 00 00 00 00 3F
[1663092212.433928] debug    | SerialAgentLinux.cpp | send_message             | [** <<SER>> **]        | client_key: 0x77247145, len: 13, data: 
0000: 81 00 00 00 0A 01 05 00 99 01 00 00 80
[1663092212.586321] debug    | SerialAgentLinux.cpp | recv_message             | [==>> SER <<==]        | client_key: 0x77247145, len: 32, data: 
0000: 81 80 99 01 07 01 18 00 01 A3 00 05 0B 00 00 00 74 65 73 74 5F 6C 61 62 65 6C 00 6D 00 00 00 3F
[1663092212.586695] debug    | DataWriter.cpp     | write                    | [** <<DDS>> **]        | client_key: 0x00000000, len: 20, data: 
0000: 0B 00 00 00 74 65 73 74 5F 6C 61 62 65 6C 00 6D 00 00 00 3F
[1663092212.586837] debug    | SerialAgentLinux.cpp | send_message             | [** <<SER>> **]        | client_key: 0x77247145, len: 13, data: 
0000: 81 00 00 ...