I just did a semi-stand development using rodinal on two 120 film rolls. My problem is, there are these small unexposed (clear) "spots" at the top of most frames on one roll of film. It only happened on one roll (Tri-X), my other roll developed fine (Arista EDU Ultra 100).

I developed both rolls at the same time in separate tanks. Both tanks had 600 ml. of 100:1 Rodinal.

Just wondering what went wrong.