Found that was a known bug for the greeting recordings. I was having issues with the messages being left in a MB for a program call Datel. Seems Avaya has a bug patch for your issue and they also have a ini file change for mine.
IPOLNX 11.1.0.1.0 build 95
Problem Clarification
Customer cannot play recordings after copying them out of the VMPro Accounts folder
Cause
.opus files are hashed (encrypted) by default now
Solution
Edit vmpro_settings.ini using CLI as root to change recordings to WAV format (insecure).
# nano /etc/vmpro_settings.ini
Change to (default is Y): UseOpusForRecordings=N
Save file (CTRL + X, Y, ENTER), then restart voicemail pro services
# service vmrpo restart
Mike