This a blog may help you to narrow down the issue. I have see above issue with few customers recently.

Skype for business CQD on-premise deployment by default will not add the category for third party endpoints. Following article may be helpful for adding a new category for third party endpoints.

Skype for business server fabric traces are enabled by default. You can find the fabric traces in following location; C:\ProgramData\Windows Fabric\Log\Traces. There is a possibility, some strange fabric issues can fill up your system drive space. Following article may help you to reduce the fabric traces to one day.

This document may be helpful when setting up SQL profiler tracing on Lync/SFB servers.

This article may help you to understand the client behavior when adding extension in skype for business 2016 contact card. I have installed SFB 2016 version 16.0.4266.1001 and SFB 2015 CU3 as backend.

This article may help you to understand the behavior when setting up SFB 2015 EE pool backend with default SQL instance and custom SQL ports and paired. The idea was to test the CMS failover and DR with above setup.

I have static meeting configuration turned on in SFB meeting policy, however if you set to remember previous configuration in client registry, outlook addin will start with dynamic meeting. This blog may help you to assign static meeting via client registry.

Saleesh Neduvayalil 3/26/2018 8:22:33 PM

This document may be helpful for troubleshooting CQD installation and configuration related issues. I have captured few common issues observed during CQD deployment and configuration.