Gnome partially stops responding to mouse, keyboard

I'm running **RHEL** Workstation 7.6. Ever since I set it up in November, I've had an ongoing issue with my system (and this is my daily desktop). - On occasion, I'm unable to click on anything. I can alt-tab, and I can type in windows. The mouse will move but clicking does nothing. - The keyboard mostly works but, say in a terminal window, I hold down the Alt key. The menu (File, Edit, View...) lights up but if I then hit Alt-F, to open the File menu, nothing happens. - Sometimes I can click on tabs in Firefox and they change - but I can't actually bring Firefox into the foreground, nor click the X to close it. - If I go to TTY2 (Ctrl-Aalt-F2) and then back to TTY1, it fixes it. Until the next time. Sometimes the fix only lasts for seconds but, if I keep trying, it will be okay for a long time - many minutes or hours. Some log entries while it's acting up. The first one occurs any time I click on a gnome-shell window while it's broken:

Feb 22 08:16:33 mybox gnome-shell: pushModal: invocation of begin_modal failed

Feb 22 08:17:38 mybox autokey-gtk.desktop: X protocol error:
Feb 22 08:17:38 mybox autokey-gtk.desktop: : code = 3, resource_id = Xlib.xobject.resource.Resource(0x00e11c6b), sequence_number = 46319, major_opcode = 33, minor_opcode = 0

Feb 22 08:17:50 mybox gnome-shell: g_array_unref: assertion 'array' failed