=4468 I would humbly suggest that insufficient 'pitch rate' in the early stages of the second half of the manoeuver is quite likely to provide a clue?.
You can't make that assumption without knowing the entry speed into the manoeuvre and the the g-force applied during it; we know neither.
If there was plenty of energy available at the top, then a higher 'pitch rate' is possible. But in a low energy state at the apex, the aircraft needs to be gently nursed over the top to allow the speed to recover with the aid of gravity and thrust. Any attempt to increase the 'pitch rate' prematurely will cause a massive rise in drag and loss of lift, and make matters worse.