Restarting domoticz, zigbee2mqtt and mosquitto in different orders did not solve my issue. Tried many times, many orders.
Rebooting the Raspberry pi that is hosting my domoticz setup and after that restarting the different services did not solve my problem.

I did check in MQTT Explorer that when using zigbee2mqtt I saw that there were messages transmitted, none when using Domoticz and it was reporting the error message. I did try and exlude my devices and inlude them again and then they worked for a short time in Domoticz but then again failed. But now ...

I have exactley the same problem. I have both zwavejs2mqtt and zigbe2mqtt working since a long time Domoticz. After upgrading all my IKEA led driver device stopped working with the same error message, "Error sending switch command, check device/hardware (idx=xxxx) !". All other zigbee devices, IKEA ...