Same problem. Very easy to test/reproduce doing:
$ light-locker-command -l
I can return to my session doing Ctrl+Alt+F1 + Ctrl+Alt+F7 and waiting unlock for the greeter.
Lubuntu 18.04.3 64 bit fresh install + updates
$ lsb_release -d Description: Ubuntu 18.04.3 LTS
$ uname -rm 5.0.0-27-generic x86_64
Acer TravelMate B118-M (TMB118-M-C4AL manufactured date 2019/05/23)
Same problem. Very easy to test/reproduce doing:
$ light-locker- command -l
I can return to my session doing Ctrl+Alt+F1 + Ctrl+Alt+F7 and waiting unlock for the greeter.
Lubuntu 18.04.3 64 bit fresh install + updates
$ lsb_release -d
Description: Ubuntu 18.04.3 LTS
$ uname -rm
5.0.0-27-generic x86_64
Acer TravelMate B118-M (TMB118-M-C4AL manufactured date 2019/05/23)