A solutions architect launched multiple EC2 instances within a placement group in a single Availability Zone. Under increased load, the architect tried to add more instances to the placement group but received an insufficient capacity error. What should the architect do to troubleshoot and resolve this problem?

When you receive an insufficient capacity error for a placement group, it means there isn't enough unreserved capacity to launch new instances with your specific requirements. Stopping and starting instances can migrate them to new underlying hardware, potentially freeing up space or allowing the new instances to be provisioned. This is a common troubleshooting step for capacity issues within placement groups. Using a spread placement group would not resolve the capacity issue within the existing group and is designed for fault tolerance across different hardware, not for increasing capacity within a single group. Creating a new placement group and merging it is not an AWS feature. Launching instances as Dedicated Hosts is a different pricing and tenancy model and would not resolve an insufficient capacity error within a shared placement group.