Determine if the number of EC2 On-Demand instances is close to the regional vCPU based limit.
AWS limits accounts to certain numbers of resources per region. Exceeding those limits could prevent resources from launching.
EC2 automatically increases On Demand Instance limits based on usage, limit increases can be requested via the Limits Page on Amazon EC2 console, the EC2 service page on the Service Quotas console, or the Service Quotas API/CLI.