Arduino and NRF24L01+ Ack Issue

I am having a transmitter with arduino Nano + NRF24L01+ module and another as receiver with Arduino Uno + NRF24L01+.

I am sending the message from transmitter with setAutoAck(true) and setRetries(15,15).

settings are same on the receiver side as well.

My receiver is also sending back the message as soon as it receives it. Basically I am using pingpair_dyn example from RF24 library.

While transmitting I also check the bool flag returned by write method.

My observation is that sometimes receiver does not receive the message but still I get return value from write method as true. At some other time I get return from write as false although my receiver has received the message and transmitter has also received the ack payload. On receiver side I am checking the received message by printing on Serial console.
This leads to wrong assumption that message has been received by receiver.

What could be the problem, please help. I using library at

GitHub - maniacbug/RF24: Arduino driver for nRF24L01 and examples form this library.

Is the autoack from NRF24L01+ is not reliable?

Appreciate any help on this.