Here are a few reasons why you might not be able to see a user's VoiceThread comment:

1. The user mistakenly posted a private reply. The user needs to repost their comment and then delete the private one.
2. The VoiceThread has comment moderation turned on. The VoiceThread creator has to approve the comments, or they can turn off comment moderation. 
3. The user deleted their comment after saving it.