Elk 6051 CO detector Transmitter loss

A few months ago we added 11 wireless devices to our Elk M1 system, including 4 CO detectors.  One CO detector in a bedroom kept giving Transmitter loss errors, was eventually replaced with no further errors.  Now a different 6051 is giving Transmitter errors about once every 3-4 weeks clearing after a day or so.  Are there issues with these detectors?  How can I quickly clear the error?  Is this device also faulty.  Checked installed firmware with Elk tech and was up to date.  Thanks.