Is this user in a remote office? I have seen issues with latency causing issues with blank voicemails. Could also be a TSP issue, but if this is the only person with the problem, then I would doubt it.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...