BUG REPORT

1. Please describe the issue you observed:

• What did you do (The steps to reproduce)?
  consuming failed, and send back to the broker
• What did you expect to see?
  this msg can be re-consumed again.
• What did you see instead?
  this msg lost

2. Please tell us about your environment:

• What is your OS?
  macos 10.14
• What is your client version?
  cpp 1.2.4
• What is your RocketMQ version?
  4.6.0

3. Other information (e.g. detailed explanation, logs, related issues, suggestions on how to fix, etc):