Rangefinder
does use key events, in order to change the mils/degrees values shown (press R to cycle through them).
Sight Adjust, like most things, steals the key event handlers for itself, not allowing others to share it. To be compatible with SPON Core, use
Shole's DEH, which includes a fixed version of the sight-adjustment that will be compatible with SPON. It also includes Shole's own NVG addon which is quite nice.