Window Management - External Right 50% stopped working

I sue the WIndow Management Palette all the time and in the last month or so the External Right 50% stopped working.

The details are identical to External Left 50% expect the command SCREENVISIBLE(External,Left) (left instead of right)

When executed all it does is move the window to the main display left 50%
Does anyone know what might be happening to suddenly have this stop working?

Just tested it, and for me it moves the window over the right edge of the external display:


KM 9.0.4, OS 10.15.3; main screen is an iMac 27″, external is a non-HD 24″.

My main display is MacBook Air (Retina, 13-inch, 2018) Intel UHD Graphics 617 1536 MB
External is old Samsung 24 in S24C57OHL/ZA
I have tried moving the external to right etc.. No luck