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When uptime crosses a multiple of 2^32 milliseconds (~49.7 days), windows stop responding to keyboard and mouse events. Restarting X clears the problem (until the uptime passes another ~49.7 days). This was originally observed with gnome-session, but it is also observable in mutter, and the latter was easier to test.

Here is my basic testing process. As it is difficult to manipulate the system's monotonic clock, I used a hacked version of the Xorg server that would use "wall" time for its clock instead of the system's monotonic clock. With this "wall" clock, an overflow/wrap-around event occurs around Jan 16 2018 17:24:15 UTC.

1. Set the date to a few minutes before the overflow time
2. Start up [hacked] Xorg
3. Start up mutter
4. Start up a couple of regular X clients (e.g. xterm, xlogo)
5. Hit Alt-Tab several times to switch between windows
6. Wait fot the clock overflow event to pass
7. Hit Alt-Tab several times to switch between windows

• Expected result: focus switches with each Alt-Tab
• Actual result: focus switches only the first time, after which key presses and button presses have no effect