fluent-bit: [Alpine Linux] fluent-bit spamming "[msgpack2json] unknown msgpack type 1970433894" to log

I have no idea what’s going on.

In the span of a few seconds fluent-bit generated a 16M log file consisting of:

[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894
[2017/09/17 23:32:37] [ warn] [msgpack2json] unknown msgpack type 1970433894

Am using Docker version 17.06.2-ce, build cec0b72, with fluent-bit version v0.12.2.

My dedicated container for logs contains this:

CMD fluent-bit -c /home/unpriv/log_to_files.conf

The config file contains this:

[SERVICE]
    Log_File  /home/unpriv/logs/fluent-bit.log

[INPUT]
    Name    forward
    Listen  0.0.0.0
    Port    24224

[OUTPUT]
    Name    file
    Match   *

[OUTPUT]
    Name    stdout

The /home/unpriv/logs/fluent-bit.log is the file containing the 16M worth of spammed msgpack2json messages.

The docker-compose.yml contains this:

version: "3.3"
services:
  mariadb:
    build: mariadb
    logging:
      driver: fluentd
      options:
        tag: "{{.Name}}-{{.ImageID}}"
    ports:
      - "3306:3306"
    depends_on:
      - logs
    environment:
      - MYSQL_ROOT_PASSWORD=password
    volumes:
      - ./vol/mariadb:/var/lib/mysql:delegated
  logs:
    build: logs
    restart: on-failure
    ports:
      - "24224:24224"
    volumes:
      - ./vol/logs:/home/unpriv/logs

It wasn’t doing this before. No idea why it’s happening now.