Anything I might say as to the cause of the failure would be pure speculation on my part. In other words, I don't know. Especially not from long distance efforts to diagnose the problem.
Partial failures of optical drives are not really rare. We see them fairly often. Your drive uses a different laser for reading and burning Blu-ray, so this one component may have simply gone bad.
If you think the firmware update had something to do with the failure, you can try reflashing the drive.