Strange MQTT exceptions - possible memory corruption?

[ldrolez]

CircuitPython version and board name

Adafruit CircuitPython 10.1.3 on 2026-02-21; Wemos Lolin C3 Mini with ESP32-C3FH4

Code/REPL

import asyncio
import wifi
import socketpool
import ssl
import adafruit_minimqtt.adafruit_minimqtt as MQTT
import usyslog

BROKER      = "192.168.0.1"
MQTT_PORT   = 1883
MQTT_TOPICS = [
    "inverter/total/P_AC",
    "battery/1/relay/set",
    "battery/2/relay/set",
]

sl = usyslog.UDPClient(socketpool.SocketPool(wifi.radio), ip='192.168.0.1', tag='battery')

def log(msg):
    try:
        sl.info(msg)
    except Exception:
        print(msg)

def handle_message(client, topic, message):
    if topic == "inverter/total/P_AC":
        power_ac = float(message)
        log(f"AC power: {power_ac} W")

    elif topic == "battery/1/relay/set":
        if message == "ON":
            log("Relay 1: turning ON")
        else:
            log("Relay 1: turning OFF")

    elif topic == "battery/2/relay/set":
        if message == "ON":
            log("Relay 2: turning ON")
        else:
            log("Relay 2: turning OFF")

async def mqtt_receive_task():
    pool    = socketpool.SocketPool(wifi.radio)
    ssl_ctx = ssl.create_default_context()

    client = MQTT.MQTT(
        broker=BROKER,
        port=MQTT_PORT,
        socket_pool=pool,
        ssl_context=ssl_ctx,
    )
    client.on_message = handle_message

    client.connect()
    client.subscribe([(topic, 0) for topic in MQTT_TOPICS])
    log("MQTT connected and subscribed.")

    while True:
        try:
            client.loop(timeout=1)
        except Exception as e:
            log(f"MQTT error: {e} – reconnecting…")
            try:
                client.reconnect()
            except Exception as re:
                log(f"Reconnect failed: {re}")
        await asyncio.sleep(9)

async def main():
    await mqtt_receive_task()

asyncio.run(main())

Behavior

After some time, 12 to 24 hours:
MQTT error: MMQTTException('Topic length 11830 in PUBLISH packet exceeds remaining length 48 - 2', None);

Description

After this exception the program becomes more and more unstable and just crashes without any error message.
I suspect a memory corruption since I use the mosquitto MQTT server with other project, without any problems, but where?
Tested with Circuitpython 10.1.3 and 10.1.4.
Two different boards tested.

Additional information

No response