Why BBP capture distorted singal sometimes?


I am debuging AD9363 Rx path, and Rx gain setting is   : AGC inner threshold is about -9dBFS and Rx FIR digtal gain is 6dB.

 Rx input is single carrier with -68dBm power ,  why sometimes BBP capture  distorted singal and  at the same time BBP capture digital value(combined p11:p0) is  >2047 or < -2047.

I am looking forward to hearing from you.

Best Regards!