I have similar issue, but I do not get the unlock dialog even after the Ctrl-Alt-F1 Ctrl-Alt-F7 trick. However, the issue does not occur, if I use nouveau graphics driver instead of nvidia driver (which I had selected in Additional Drivers dialog). See also Bug #1811402
I have similar issue, but I do not get the unlock dialog even after the Ctrl-Alt-F1 Ctrl-Alt-F7 trick. However, the issue does not occur, if I use nouveau graphics driver instead of nvidia driver (which I had selected in Additional Drivers dialog). See also Bug #1811402
xfce4-screensaver is not available for 18.04