[orca-list] gnome-shell going silent

[<prayner unimelb edu au>]

Or at least I think it's gnome-shell.
This is with orca master, gnome-shell 3.28.4 on ubuntu 18.04-LTS and
using the lightdm display manager.
Logging in is pleasantly chatty.
On successfully logging in I hear "screen reader on" then silence.
alt-f2 doesn't echo or speak characters when I arrow over them.
Applications once started are fine.
things like ctrl-alt-tab which should bring up the top bar is silent
though sighted assistance says it's there. alt-tab between
applications *does* say something e.g. "emacs frame dummy text panel".
steps to reproduce
start up system, should hear from the greeter
log in
after a time system says "screen reader on"
type alt-f2 and some characters.
left-arrow back over said characters, 
As I write this it doesn't sound much like an orca problem but rather
something going odd with gnome-shell. Has anyone seen this?
Any pointers where I should look?
thanks in advance
Peter

-- 
Peter Rayner
Acting Director - Climate & Energy College <http://www.climatecollege.unimelb.edu.au>
Clean Air and Urban Landscapes NESP hub <http://www.nespurban.edu.au>
School of Earth Sciences, University of Melbourne, 3010, Vic, Australia
mobile +61 402 752 379, skype: petermorag 
zoom id 4431343191, join at  <https://unimelb.zoom.us/j/4431343191>
mail-to: prayner unimelb edu au TWITTER: @raynerstrings