I think that the problem is a light leak, most likely due to the fit between the holder and the body.
In the 3 vertical shots, the “band” looks approximately normal and the rest of the scene is fogged.
The fogged area is strongest on the lower left side of the picture. With the camera in vertical orientation, that corresponds to the upper right. That is where I suspect that the light leak is coming from.
In horizontal orientation the leak will be on the bottom edge to the right. With the leak along the bottom edge, the amount of light reflected by the ground is likely considerably less than when the camera is in vertical orientation with the gap able to “see” the sky to the upper right.
You can verify the leak by attaching the holder in a relatively darkened room, removing the dark slide, covering the back of the camera and holder with a dark cloth, making the vertical format exposure, and returning to the darkened room to replace the slide.
If the film shows no light leak then you’ll know that you’ve found the problem.
You may want to re-engineer the way the camera seals against the holder.