Sometimes, your Internet connection may appear to be working, but it’s actually dropping packets of data occasionally. Since the voice files are very large, this can cause voice download to fail.
The first thing you want to check is whether you’re downloading any data at all. When you press “Download”, do you see any progress? Is the blue bar growing? If so, you can keep pressing on the “Download” button until it completes. The voice downloader resumes from the point where it failed.
If after you press “Download” and there is no progress — just an error message — then you should find another WiFi network and download the voice there.
Last, please make sure that you’re not running any software on your device that interferes with network traffic. VPN, and other network monitoring and security software may cause issues.