When restarting the mattermost server (systemctl restart mattermost), the log file gives me a hint:
{"timestamp":"2024-10-27 10:05:16.677 +01:00","level":"info","msg":"Post.Message has size restrictions","caller":"sqlstore/post_store.go:2615","max_characters":16383,"max_bytes":65535}
I’m using a postgres backend. Can this be the issue ?