Nice job, thanks!
Here are the 3 images side by side for easier comparing:
Rodinal-1-100.jpg1+100 Rodinal-1-25.jpg1+25 Rodinal-1-25-Salt.jpg1+25 with salt Rodinal-1-100-Salt.jpg 1+100 with Salt
It is possible that the sun was gone in image #3 (with Salt)? I don't see the shadow of the ladder anymore.
If you used the same exposure time, then this could explain the darker image.
Are you planning on printing the images in an identical way?