/usr/bin/Xwayland:6:wl_proxy_destroy:wl_callback_destroy:xwl_present_sync_callback:ffi_call_unix64:ffi_call

[errors.ubuntu.com bug bridge]

The Ubuntu Error Tracker has been receiving reports about a problem regarding xorg-server. This problem was most recently seen with package version 2:1.20.4-1ubuntu2, the problem page at https://errors.ubuntu.com/problem/008c7bd0fdc996890cce5f67e5f0214f280aefd8 contains more details, including versions of packages affected, stacktrace or traceback, and individual crash reports.
If you do not have access to the Ubuntu Error Tracker and are a software developer, you can request it at http://forms.canonical.com/reports/.