Hi,
Did the issue happen with a Persistent Chat or just a multiple IM?
Did the issue happen for just one user or for multiple users?
If the issue happen just for one user, try to test with other SFB client on other PCs. If the issue just happen on single SFB client, make sure SFB client update to the latest version.
If the issue happen with multiple SFB users with multiple SFB clients, then try to restart FE Services and make sure SFB Server update to the latest version and then test again.
Best Regards
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Eason Huang
TechNet Community Support
