Moving the fastest line with shift & arrow keys not working

[redapg]

None of the combinations work. Tried shift & left alt & ctrl & alt.

Hmmm, that's strange.
With left Ctrl + left Alt + left and right Arrow, i can move the Pathes slowly.
Did you try it a bit longer?
It moves REALLY slow, so you maybe didn't notice the Movement.
What you could do, as a Test, before you start the DevMode, rename the ModDevs player.JSON into player_Backup.JSON for Example, to get a fresh one generated when you start the DevMode.
Does it work with that?