On November 2016, Lync 2013 (Skype for Business 2015) customers start reporting cases of duplicate of IM messages.
The issue started appearing after the installation of November 2016 client update (KB3127934) and it affects the receiver only.
Steps to recreate the issue (credits go to Alex) :
- Send an IM to an user
- Do not open the IM toast on the receiving user
- Send another (or more) IM the that user
- Open the notification toast of the receiving user and you will noticed that only the first IM line sent is not repeated
The issue does not occur when the IM conversion window is open.
Applying the December 6, 2016, update for Skype for Business 2015 (Lync 2013) (KB3127976) also causes the same issue.
Skype for Business 2016 clients are also affected on the same way by their corresponding monthly cumulative updates. There is an oldest thread on Microsoft community that was reopened by another 2 persons that report the same behaviour and uninstalling the KB3127934 would solve the issue.
Apply the January 3, 2017 update for Skype for Business 2015 (Lync 2013) (KB3141468) or Skype for Business 2016 (KB3128049).
It is mentioned on the resolved issue list (no root cause provided):
“Assume that you send continuous instant messages (IMs) to a user in Microsoft Skype for Business 2015 (Lync 2013). Then you allow the toast notification window to be auto accepted. In the conversation window, you find every item but first gets duplicated. Also, in the Conversation History in Microsoft Outlook, you find that the conversation window shows duplicated IMs. “
I successfully tested and confirmed that it solves.