hard to say like this but here are a few troubleshooting steps you can try and let me know what did you found out:

1. Ensure that the Chat app is actually added to the group conversation. Try mentioning the bot directly using @your-bot-name to check if it recognizes the app.

2. Ensure your appsscript.json includes the required scopes for Google Chat:

   {"timeZone": "America/New_York","dependencies": {},"webapp": {"executeAs": "USER_DEPLOYING","access": "ANYONE"},"oauthScopes"["https://www.googleapis.com/auth/chat.bot"]}

3. If you used the "Editor Add-on" deployment, try deploying as a "Web app" instead: Go to Apps Script → Deploy → New Deployment. Select Web app. Set Who has access to Anyone or Anyone within your domain. Copy the URL and register it in Google Cloud Console under the Chat App's configuration.

4. Go to Google Cloud Console: Navigate to IAM & Admin → IAM. Ensure the service account linked to your Chat bot has the roles/chat.botUser or roles/chat.appAdmin role.

5. In Apps Script, go to Executions and check for errors. If the bot is getting triggered but not responding, there might be an issue in your doPost(e) or doGet(e) function.

6. Try removing and re-adding the bot to the conversation to refresh permissions.

7. Create a new group conversation and add the bot to see if it behaves differently.

could you check if any errors appear in your Google Cloud Logs? That can provide more insight into what's preventing the bot from responding.