Reason: Dropped message: QoS 0 channel not writable

Question

What does the error message "Dropped message: QoS 0 channel not writable" signify when observed in the HiveMQ control center?

Answer

The "Dropped message: QoS 0 channel not writable" notification appearing in the HiveMQ Control Center is not indicative of a broker error. As per the MQTT specification, QoS 0 messages have no delivery guarantee and may be dropped. The purpose of this notification is to alert users to potential concerns related to slow-consuming clients.

When your clients are consuming slowly or cannot handle the load on subscribed topics individually then a possible solution is to use shared subscriptions.