Hi Ethan Lexus,
For this issue, please try the following troubleshooting steps:
1.Please check if the issue only appeared on the specific client, try to test with another normal computer.
2.Try to delete SFB cache files and test again: %userprofile%\AppData\Local\Microsoft\Office\16.0\Lync\sip_UserName@Domain.com
3. Perform clean boot on your computer: https://support.microsoft.com/en-us/kb/929135
4. Install the latest update for your SFB client.
Regards,
Alice Wang
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