Consider the following scenario in a Microsoft Skype for Business Server 2019 environment:
You have installed the July 2019 cumulative update 7.0.2046.123 for Skype for Business Server 2019, Conferencing Server.
You have a third-party contact center or other application that's based on Microsoft Unified Communications Managed API (UCMA). UCMA is used to manage conferences and adjust Audio/Video Conferencing Server audio routes.
In this scenario, you randomly experience conferencing audio/video failures. Additionally, you may notice that the following event log entry is recorded on one or more of your Skype for Business 2019 Front End servers:
Source: LS Audio-Video Conferencing Server
Message: The Audio/Video Conferencing Server has failed to create a conference.
Conference URI: URI;gruu;opaque=app:conf:focus:id:abcdefgh Exception: Media Processor instance is not available to service this request
This issue occurs because the Audio/Video Conferencing Server experiences a deadlock under certain timing conditions.
To work around this issue, downgrade the Conferencing Server to the RTM version. To do this, remove KB 4499969.
Microsoft is researching this problem and will post more information in this article when it becomes available.