This falls into the “oh wonderful” category…
https://technet.microsoft.com/en-us/library/security/ms16-065.aspx breaks Office Web Apps for internal users. External users seem to be unaffected.
Conferencing modalities no longer function in Lync Server 2010, Lync Server 2013, or Skype for Business Server 2015 after you install Security Bulletin MS16-065Here is a
And people wonder why I always advise waiting 90 days or so before patching Lync and SfB host servers.
The documented update in the article is KB3156757, but the actual KB installed was KB3156756. Which also is associated with MS16-065.