I noticed this account plays in 3 different game regions. The most likely cause for the missing friends list is that they were added in a different region for the game. My advice would be to log out of the Blizzard app then back in using each different region until you find where the friends were added at.
I also checked the Voice Chat errors submitted by the account. I noticed some RTP timeout errors. This suggests the voice chat service is having trouble staying connected.
If the voice chat is unable to connect it could be a security protocol treating the voice chat service differently than the rest of the game ( yes it runs two separate network connections) - My advice here would be to disable any third party security software and quality of service programs on the computer. Restarting the networking devices may also help!
I do hope the info helps. If there’s anything else you might need just let us know.