AWS EC2 Instances Removed

You could look int Cloudtrail. See this as an example:https://repost.aws/knowledge-center/ec2-windows-identify-stop-reboot

AWS CloudTrail service captures the API calls made by a user, role, or an AWS service from your AWS account. Using this service, you can narrow down how the instance was terminated. Lookup for the API call "TerminateInstances ". Refer to the below link. - https://repost.aws/knowledge-center/troubleshoot-ec2-instance-terminate

An EC2 instance is created in a specific AWS Region. Are you sure you're viewing the Region in which you created the instances?

You can use the EC2 Global View to see your instances across all Regions. For more information about EC2 Global View, please see the following link: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/global-view.html