Hi ,
Where do you have the SFB account hosted is that online or Onpremise? Check if you have a different machine to try the behavior. You can also uninstall the version and install a fresh version if you suspect anything with the software. Clear the user
profile in your computer and create a new one by logging in again
Delete local cache files on client computer.
%userprofile%\AppData\Local\Microsoft\Office\15.0\Lync\sip_UserName@Domain.com
Registry Key: HKCU\Software\Microsoft\Office\15.0\Lync\UserName@Domain.com
Linus || Please mark posts as answers/helpful if it answers your question.