Comment 3 for bug 1561345

My above traceback is slightly different than the OP but there seem to be some known issues in this section of code also with similar backtraces:

"'NoneType' object has no attribute 'grab_focus'"
  * https://bugs.launchpad.net/ubuntu/+source/terminator/+bug/1561345
  * https://bugzilla.redhat.com/show_bug.cgi?id=1898476
  * https://github.com/gnome-terminator/terminator/pull/145/commits/9edefb6f3285fa236656bcc2440661d1a107174b
  * https://errors.ubuntu.com/problem/f0c07815340e8b5e1e401bead074eaf287e8ca00

"'VPaned' object has no attribute 'is_child_notebook'"
  * https://errors.ubuntu.com/problem/9aa9259838a67d8c24c342b106efd841b516340b
  * https://bugs.launchpad.net/ubuntu/+source/terminator/+bug/1931317
  * https://bugzilla.redhat.com/show_bug.cgi?id=1898476

This may be a suitable fix:
            if focus_sibling:
                first_term_sibling.grab_focus()
            elif not sibling.get_toplevel().is_child_notebook():
                try:
                    Terminator().find_terminal_by_uuid(sibling.get_toplevel().last_active_term.urn).grab_focus()
  except AttributeError:
                    if sibling.get_toplevel().last_active_term:
                        dbg('cannot find terminal with uuid: %s' % sibling.get_toplevel().last_active_term.urn)
                    else:
                        dbg('last active terminal does not have a uuid')