Copilot Studio consistent System Error issue

I have built an agent that invokes a Power Automate flow as a tool. Inside the flow, I'm using the Execute Agent and Wait activity, which calls another agent. This execution takes around 10–15 minutes to complete, after which the flow returns the result using Respond to Agent (asynchronous response).

Although the flow completes successfully and the downstream agent finishes its execution, the calling agent still receives a System Error instead of the expected response.

Why I'm using a Flow instead of directly connecting the agent

Normally, I would connect the agent directly. However, the agent being invoked is already connected to another agent. Since agent → agent → agent chaining is not supported in Classic mode, I used a Power Automate flow as an orchestration layer to work around this limitation.

Looking for someone who have faced this issue and has any solution to this.