// PLEASE NOTE: this an next comment are re-do's of this, as my right-screen rototated during this
// PLEASE NOTE: next comment is a retry of only some of the steps in this

I booted the live thumb drive (19.04 daily described above; it hasn't been re-written).

Verified that my display.change wasn't suddenly working now (nope, no change & clicking 'apply' caused it to grey-out etc...  I took a screenshot (attached), then opened term & entered command copied from request in last (prior) comment

The command caused lots of lines to print, then paused....
I waited, then suspected the debug screen was waiting for me to do something, so I opened DISPLAY.settings

The [display.settings] window appeared to be locked (as if apply had been clicked; had I not closed it?? so I closed window)
I re-opened [display.settings] window & it seemed again to not respond, noticed a few more lines appear in debug.term.window, then noted (change of color to my right) that my right screen had rotated as I wanted!????

I'll save this locally, and then reboot & re-do this steps adding notes 

xubuntu@xubuntu:~$ XFSETTINGSD_DEBUG=1 xfsettingsd --replace --no-daemon

(xfsettingsd:4710): xfsettingsd-WARNING **: 11:17:35.343: Property "/Gdk/WindowScalingFactor" has an unsupported type "guint".
xfce4-settings(xsettings): _XSETTINGS_S0 registered on screen 0
xfce4-settings(xsettings): 31 settings changed (serial=0, len=1256)
xfce4-settings(xsettings): resource manager (xft) changed (len=1330)
xfce4-settings(displays): Detected CRTC 79.
xfce4-settings(displays): Detected CRTC 80.
xfce4-settings(displays): Detected output 82 DVI-0.
xfce4-settings(displays): Detected output 83 DVI-1.
xfce4-settings(displays): CRTC 79 assigned to DVI-0.
xfce4-settings(displays): CRTC 79, output list[0] -> 82.
xfce4-settings(displays): CRTC 80 assigned to DVI-1.
xfce4-settings(displays): CRTC 80, output list[0] -> 83.
xfce4-settings(displays): Total 2 active output(s).
xfce4-settings(displays): Normalized CRTC 79: size=1280x1024, pos=0x0.
xfce4-settings(displays): Normalized CRTC 80: size=1024x1280, pos=1280x0.
xfce4-settings(displays): CRTC 80 must be temporarily disabled.
xfce4-settings(displays): Disabling CRTC 80.
xfce4-settings(displays): min_h = 200, min_w = 320, max_h = 8192, max_w = 8192, prev_h = 1024, prev_w = 2560, prev_hmm = 270, prev_wmm = 677, h = 1280, w = 2304, hmm = 339, wmm = 610.
xfce4-settings(displays): Applying desktop dimensions: 2304x1280 (px), 610x339 (mm).
xfce4-settings(displays): Configuring CRTC 79.
xfce4-settings(displays): Applying changes to CRTC 79.
xfce4-settings(displays): Applying CRTC 79 Transform: x=1.000000 y=1.000000, filter=nearest.
xfce4-settings(displays): Configuring CRTC 80.
xfce4-settings(displays): Applying changes to CRTC 80.
xfce4-settings(displays): Applying CRTC 80 Transform: x=1.000000 y=1.000000, filter=nearest.
xfce4-settings(pointers): initialized xi 2.3
xfce4-settings(keyboards): initialized xkb 1.0
xfce4-settings(keyboards): set auto repeat on
xfce4-settings(keyboards): set key repeat (delay=500, rate=50)
xfce4-settings(keyboards): don't set numlock
xfce4-settings(accessibility): AccessXKeys disabled
xfce4-settings(accessibility): stickykeys disabled
xfce4-settings(accessibility): slowkeys disabled
xfce4-settings(accessibility): bouncekeys disabled
xfce4-settings(accessibility): mousekeys disabled
xfce4-settings(keyboard-shortcuts): 31 shortcuts loaded
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 79.
xfce4-settings(displays): Detected CRTC 80.
xfce4-settings(displays): Detected output 82 DVI-0.
xfce4-settings(displays): Detected output 83 DVI-1.
xfce4-settings(displays): Noutput: before = 2, after = 2.
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 79.
xfce4-settings(displays): Detected CRTC 80.
xfce4-settings(displays): Detected output 82 DVI-0.
xfce4-settings(displays): Detected output 83 DVI-1.
xfce4-settings(displays): Noutput: before = 2, after = 2.
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 79.
xfce4-settings(displays): Detected CRTC 80.
xfce4-settings(displays): Detected output 82 DVI-0.
xfce4-settings(displays): Detected output 83 DVI-1.
xfce4-settings(displays): Noutput: before = 2, after = 2.
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 79.
xfce4-settings(displays): Detected CRTC 80.
xfce4-settings(displays): Detected output 82 DVI-0.
xfce4-settings(displays): Detected output 83 DVI-1.
xfce4-settings(displays): Noutput: before = 2, after = 2.
xfce4-settings(fontconfig): monitoring 163 paths
xfce4-settings(workspaces): 1 desktop names set from xfconf
xfce4-settings(displays): CRTC 79 assigned to DVI-0.
xfce4-settings(displays): CRTC 79, output list[0] -> 82.
xfce4-settings(displays): CRTC 80 assigned to DVI-1.
xfce4-settings(displays): CRTC 80, output list[0] -> 83.
xfce4-settings(displays): Total 2 active output(s).
xfce4-settings(displays): Normalized CRTC 79: size=1280x1024, pos=0x0.
xfce4-settings(displays): Normalized CRTC 80: size=1024x1280, pos=1280x0.
xfce4-settings(displays): min_h = 200, min_w = 320, max_h = 8192, max_w = 8192, prev_h = 1280, prev_w = 2304, prev_hmm = 339, prev_wmm = 610, h = 1280, w = 2304, hmm = 339, wmm = 610.
xfce4-settings(displays): Configuring CRTC 79.
xfce4-settings(displays): Applying changes to CRTC 79.
xfce4-settings(displays): Applying CRTC 79 Transform: x=1.000000 y=1.000000, filter=nearest.
xfce4-settings(displays): Configuring CRTC 80.
xfce4-settings(displays): Applying changes to CRTC 80.
xfce4-settings(displays): Applying CRTC 80 Transform: x=1.000000 y=1.000000, filter=nearest.

// sorry I didn't note at which point I did steps for in the logged output display at term