When your payload type container starts up, it connects to the rabbitMQ broker system and sends a heartbeat notification to Mythic. Mythic then tries to look up the associated payload type and, if it can find it, will update the last_checkin time. However, if Mythic cannot find the payload type, then it'll issue a "sync" message to the container. Similarly, when a container starts up, the first thing it does upon successfully connecting to the rabbitMQ broker system is to send its own synced data.