What does this user do before this issue happened?
Above all, it is suggested to clear Skype for Business client cache as below:
- Right click the Windows icon and open the Run bar
- Type in: %localappdata%\Microsoft\Office\1x.0\Lync\ folder
- Delete the sip profile folder.
- Go into the Tracing folder, delete all files.
Then, delete your sign-in info in the sign in interface.
Besides, perform a clean boot to avoid third party programs’ effect.
Make sure that your client version is the latest one.
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