Symptoms
In Microsoft Skype for Business Server 2019 or Skype for Business Server 2015, a Skype for Business client user still receives a missed call notification even though the call was answered by other telephony systems (for example, the Alcatel telephony system).
Resolution
To fix this issue, install one of the following updates:
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The September 2020 cumulative update 7.0.2046.244 for Skype for Business Server 2019, Front End Server and Edge Server.
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The August 2021 cumulative update 6.0.9319.619 for Skype for Business Server 2015, Front End Server and Edge Server.
