Amazon Web Services (AWS), is a collection of remote computing services, also called web services, that make up a cloud-computing platform operated from 11 geographical regions across the world. The most central and well-known of these services include Amazon Elastic Compute Cloud, also known as "EC2", and Amazon Simple Storage Service, also known as "S3". Other services include Elastic MapReduce (EMR), Route 53 (a DNS web service), provides a highly available and scalable Domain Name System (DNS) web service, Virtual Private Cloud (VPC), storage, database, deployment and application services.
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Either way, it's unusual. However, I have seen some weird behavior before if the AWS API is acting out.
one thing to try, is another browser first, to see if it's a UI issue. Other than that, if the machine is currently in a full running state or it's pending a stop, you will want to either post in the AWS EC2 forum:
https://forums.aws.amazon.com/forum.jspa?forumID=30
Or open a ticket/chat with support.
If your instance is on faulty underlying hardware, and it is in fact in a (Stopping...) state, it could take a while before it's fully stopped, and even AWS support will tell you to wait it out, as they can't do a whole lot about it.