Oh the roll up, it is the nemesis of so many. It isn’t so much about ab strength is it is about integration and timining.
What is involved in a roll up…. well a lot
lumbopelvic rhythm —> your low back (lumbar) needs to move with the pelvis and the pelvis needs to move with the thighbones (femurs). This timinig is the major reason people struggle with the roll up
Try the roll down phase first or use a prop (a wall, some weighted balls or a band) to help you with the timing.