Hello,
We have created an agent in our environment, and the agent started to respond all questions with fall back topic. It was working 2 days ago and suddenly it encounters this issue. We have tested the questions in copilot portal, and it seems that it found the answer in the knowledge base but cut off when respond to the users.
Found the answer in the knowledge base
However, for the questions that we created the topic for, it works. So we thought we might have accidentally enabled 'Classic' orchestration in the setting, but it is generative AI orchestration.

Since it happens a few days ago, we were wondering if Microsoft did any breaking changes updates to copilot studio and anyone experience similar situation like us. Thanks in advance for your help!