Read the reviews?
I think what is going on there is the classic trickle charge detection problem, and the regulator discontinuity problems suffered with Apple products, Apple sometimes struggle with other than supplied mains charger. We see similar issues with the Fusion. Apples products want to know the mains power is stable so if it is not then the Apple product disconnects, then the Anker product senses no device attached and stops transmitting. As the voltage from Anker is regulated it is not perfectly flat, as the battery voltage drops a notch, the regular alters its step, the Apple product senses that step and stops taking charge. Finnicky Apple!
This would be a struggle for anyone, not just Anker.
So a little unfair on Anker but also a challenge for Anker as Apple products are popular.