Hi,
First of all, I would recommend checking if there are any faults. In Kucher there is the faults counter. You can check if the fault counter doesn’t increase or you can check the logs. As the propeller is big, it requires more current during transients for accelerating and decelerating the motor. This, in turn, can cause the hardware faults and the motor desync.
If there are no faults, you can switch to rpm control mode and tune it for more aggressive characteristics as described here. Or you can stay in the voltage control mode and increase the o.ekf.q_id and o.ekf.q_iq parameters in small steps. But be careful not to lose stability in the continuous motor spinning. You can find more information about advanced tuning in this post.