Accordian Window Shades Don't Fold Along Creases

A couple of my accordian window blinds, the opaque ones, when lifting don't fold up along the crease in a couple of sections, they flatten out as I slowly lift them from then center of the lift bar. I then have to push on the back of the blind to pop the affected section to the crease. I've left the affected blinds in the up or compressed state but the issue returns. Are these blinds strings adjusted too tight?



Thanks



Kelvin