This happened to me once I installed the newest kernel (5.1.5). When I check journalctl -p warning -b I see this, which seems like the likely culprit.
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2418]: upower.service: Failed to set up mount namespacing: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2418]: upower.service: Failed at step NAMESPACE spawning /usr/libexec/upowerd: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: upower.service: Failed with result 'exit-code'.
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: Failed to start Daemon for power management.
Jun 04 11:59:32 raijin.simulcast.ove.com gnome-shell[2146]: g_dir_open_with_errno: assertion 'path != NULL' failed
Jun 04 11:59:32 raijin.simulcast.ove.com gnome-shell[2146]: g_filename_to_utf8: assertion 'opsysstring != NULL' failed
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2425]: geoclue.service: Failed to set up mount namespacing: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2425]: geoclue.service: Failed at step NAMESPACE spawning /usr/libexec/geoclue: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: geoclue.service: Failed with result 'exit-code'.
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: Failed to start Location Lookup Service.
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2473]: upower.service: Failed to set up mount namespacing: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2473]: upower.service: Failed at step NAMESPACE spawning /usr/libexec/upowerd: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: upower.service: Failed with result 'exit-code'.
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: Failed to start Daemon for power management.
Jun 04 11:59:32 raijin.simulcast.ove.com gsd-xsettings[2440]: Failed to get current display configuration state: GDBus.Error:org.freedesktop.DBus.Error.NameHasNoOwner: Destination does not exist
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2520]: upower.service: Failed to set up mount namespacing: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2520]: upower.service: Failed at step NAMESPACE spawning /usr/libexec/upowerd: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: upower.service: Failed with result 'exit-code'.
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: Failed to start Daemon for power management.
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2533]: fprintd.service: Failed to set up mount namespacing: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2533]: fprintd.service: Failed at step NAMESPACE spawning /usr/libexec/fprintd: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: fprintd.service: Failed with result 'exit-code'.
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: Failed to start Fingerprint Authentication Daemon.
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2542]: upower.service: Failed to set up mount namespacing: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[2542]: upower.service: Failed at step NAMESPACE spawning /usr/libexec/upowerd: Permission denied
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: upower.service: Failed with result 'exit-code'.
Jun 04 11:59:32 raijin.simulcast.ove.com systemd[1]: Failed to start Daemon for power management.
Jun 04 11:59:33 raijin.simulcast.ove.com systemd[2545]: upower.service: Failed to set up mount namespacing: Permission denied
Jun 04 11:59:33 raijin.simulcast.ove.com systemd[2545]: upower.service: Failed at step NAMESPACE spawning /usr/libexec/upowerd: Permission denied
Jun 04 11:59:33 raijin.simulcast.ove.com systemd[1]: upower.service: Failed with result 'exit-code'.
Jun 04 11:59:33 raijin.simulcast.ove.com systemd[1]: Failed to start Daemon for power management.
Jun 04 11:59:33 raijin.simulcast.ove.com systemd[1]: upower.service: Start request repeated too quickly.
Jun 04 11:59:33 raijin.simulcast.ove.com systemd[1]: upower.service: Failed with result 'exit-code'.
Jun 04 11:59:33 raijin.simulcast.ove.com systemd[1]: Failed to start Daemon for power management.
All that said, I’m a bit at a loss of what to do from here to fix it. Maybe someone else has some insight?