Altium: board cutouts and multiple flex-regions
I can't really tell from the picture what you're trying to do, but I find when I'm doing rigid flex I try to draw one continuous outline in board planning mode first, including the flex sections. I do the cutouts later.

Your layout and board outline should treat the rigid and flex sections as all one board. After you have an outline defined, you should place cutouts in layout mode, then later go back to board planning mode to set your board section lines.

Keep in mind that the bend lines do nothing for fabrication files, they seem to purely be for visual effects in 3D mode.