Hi All
I believe the issue we are all having stems from another application called snip & sketch which included the ruler function. (now merged into snipping tool)
I have found an alternative for creating a straight line within snip tool if this is all you require. if you hold down the SHIFT key as you create the line it will snap at 45 degree increments.
This also applies for the arrow function, the rectangle will retain a square aspect ratio when shift is held.
I hope this helps!
Regards
Ross