I'm one of the developers for the Firestorm viewer (http://www.firestormviewer.org) for accessing Linden Lab's Second Life using OpenGL. Since a few days, we received several reports of users suddenly having severe performance issues using our program after
they temporarily task-switched to a different program. It turns out that all of these users are running Windows 10 and the issue started to arise after installing the latest Windows update KB3176938 (Windows Version 1607 Build 14393.105). After uninstalling
the update, the issue has gone away.
What happens exactly is, that for many users simply switching from our program to some other (program loses focus) and then switching back results in a drastic drop in frames per second, whereas scenes previously rendering perfectly fine are suddenly rendered with 2 FPS. When this happens appears to be rather undeterministic - for some people it already happens right at the first task switch, for others after a random amount of time and task switches.
Further details (including system specs of users affected) can be obtained from our issue tracker at http://jira.phoenixviewer.com/browse/FIRE-20034
Personally, I experienced this issue twice already in a single day after I installed KB317698 but only after a random time and number of task switches.
There are also reports of other games suddenly showing the same kind of issue, all using OpenGL apparently:
* Runescape: https://www.reddit.com/r/runescape/comments/50o7pf/kb3176938_for_windows_update_is_causing_massive/ & http://services.runescape.com/m=forum/forums.ws?415,416,704,65828403
* X-Plane 10: http://forum.aerosoft.com/index.php?/topic/114962-fps-frieren-ein-seit-windows-kb3176938-update/
I already reported this via the Feedback tool, but apparently it restricts visibility of issues to the language version of the local Windows installation, so I'm reporting this here as well so our users can add additional comments.
EDIT 07-09-2016: Microsoft has been informed by Linden Lab and is investigating the issue.