Hi Mathew,
Did the issue only appear on specific user?
Regarding this issue, please try the following troubleshooting steps:
1. Please try to rebuild outlook profile, for SFB client, clear cache files: %userprofile%\AppData\Local\Microsoft\Office\15.0\Lync\sip_UserName@Domain.com
2. Perform a clean boot on your computer:
https://support.microsoft.com/en-us/kb/929135
3. If the issue persists, please try to repair your Office.
4. Make sure your SFB client and outlook client with the latest update.
Regards,
Alice Wang
Please remember to
mark the replies as answers if they help.
If you have feedback for TechNet Subscriber Support, contact
tnmff@microsoft.com.