An offline Malfunction alert means that the particular device is having trouble communicating with the panel. In general, this is a common status and usually indicates intermittent signal trouble due to range or attenuation.
Here is a guide to troubleshooting for a Z-wave device like the T6:
It looks like in this case we may have received an email with additional context however. If you have factory reset the thermostat it would need to be deleted and relearned into the alarm panel. Factory resetting it clears its internal network data.
Follow the steps in the link below to reconnect if you have not already, including the remove device steps first to clear the old instance from the panel.