Ubuntu is a popular Linux distribution that's user-friendly and easy to use. It has a lot of features that make it a great choice for people who are new to Linux.
This issue comes from some reason. But last time when i tried to setup ubuntu i see the problem happens frequently. So i can say most of the case from new linux OS install. Giving you two quick shot method.
EBS means Elastic block Store and its available to use in EC2 instance. For EBS you are only able to increase the volume, generally is not able decrease.