A problem that the coordinator sends a large amount of data to the enddevice

Hi, We did an experiment: using a coordinator to send data to 5 enddevice very quickly.( 60ms ),  we found that when we stoped sending the data,coordinator was not working properly：

 uint8 ZMacDataReqSec( ZMacDataReq_t *pData, applySecCB_t secCB )    the function ZMacDataReqSec  was  called frequently,.but  could not alloc mem by MAC_McpsDataAlloc .

We allow packet loss, but when we stop sending, we hope that the coordinator will work properly. 

When there is a problem, what can I do to eliminate all buffered data in a violent way?

thanks