See why the characters on the computer become shorter after vertical shooting.

It is possible that the lens is out of shape. Generally, when shooting a wide-angle lens, the closer to the edge, the more prone to tensile distortion. Generally speaking, it is to lengthen the object. If the person you shoot is too close to the middle of the picture, because the surrounding objects are stretched, it will appear that the person will be shorter. This distortion is usually relatively small. Maybe you put it on the computer screen and found the problem of people getting shorter, but you didn't notice it on the LCD screen of the camera.

I hope my answer will satisfy you ~