Launching with snapshot based volume fails

I had the same issue, described it here Amazon Launch Template - Updated AMI .

tl;dr You need to keep AMI and volume's sizes the same. I had 15 GB AMI and 8 GB volume.

Ran into the same issue while mounting EBS volume to /dev/sdc on an instance (c3.2xlarge) using HVM image.

The solution which worked for me was to use an available AWS recommended device name e.g. /dev/sdf. AWS recommended device name for attaching EBS volume is /dev/sd[f-p]

For Linux/Unix instance recommended device names are /dev/sd[f-p]

Source: AWS Block Device Naming on Linux Instances