The angle of the mirror has to be out only a fraction of a millimeter for a camera to not focus correctly at infinity. And some cameras are easier than others in making this adjustment.

I had the same problem with a Yashica Contax 139 Quartz. On that camera, you have to remove the front body panel and turn a small screw to adjust the angle of the mirror.

On a Zeiss Ikon Contaflex I (and other cameras), you remove a cap on the base of the mirror box and turn a small post.