Hi kesh951,
Did this issue occur to multiple users?
To this issue, please try to rebuild SFB profile to check if the issue persist:
https://chinookcommunications.zendesk.com/hc/en-us/articles/203814180-Delete-the-Lync-SIP-profile-from-a-Windows-computer
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Best Regards,
Jim Xu
TechNet Community Support
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