Ahh ok so I may have been right for once! I was developing a complex for a minute ha. Yeah CTRL + F is deceiving as it simply creates an edge over top of the existing face. CTRL + J cuts an edge *through* the existing face.
I can confirm your issue of not getting the middle row of faces to separate from the sides by cutting seams. I’ve never seen that before. The only way I could separate it was to select the middle row of faces by themselves and hit U -> Unrwap. There’s *always* more than one way to skin a cat in Blender / CG:
