If you have a bad one. Make sure you contact support before you replace it. Once you have a RMA then then swap out with your spare. That is what I do.
They need it connected to your array to approve it quickly. If you go in to enlighten or the support link as I posted it sometimes gets approval right on the spot.
https://service.enphaseenergy.com/users/sign_in
Before you consider the microinverter dead.
Login to your Envoy just use its IP address. Go to the Administration tab.
Then to Device Conditions and Controls search for the bad device.
select the device that is causing the issue.
You can then clear gfi or send a reboot.
Sometimes this can fix a microinverter.