USRP RX overflow

[a_sweet_cat_not_salty_cat]

  Recently I use USRP B210 for wireless communication. The problem is:

  The USRP can support over 50M IQ rate. When I run the vi, the largest value of IQ rate is 7,2M. If I increase IQ rate, it will occur overflow trouble.

  "niUSRP Fetch Rx Data (CDB WDT).vi<ERR>Overflow: an internal receive buffer has filled before the data could be returned. Consider reducing the I/Q rate, increasing the Fetch rate, or increasing the number of samples per Fetch. The recommended number of samples per Fetch is a multiple of 2040."

  I discover the use of CPU is under 10%, which means the vi doesn't fully utilize the resource of computer. Theoretically, overflow problem should not occur. I think the result has a connection with niUSRP Fetch Rx Data (poly) (VI),  but I don't know how to solve it. Could anyone help me? Thank you.