A developer has built an online shopping application that is deployed on EC2 instances, which are managed by load balancers to handle traffic. This web application, consistently running the same version, is distributed across multiple EC2 instances organized within an Auto Scaling group to ensure scalability and availability. The application utilizes AWS Security Token Service (STS) to obtain temporary security credentials for AWS service access. However, it has been observed that the application ceases to function after an hour of operation.

What is the most probable reason for this problem?