SN65HVD1050: can't stable communication with 15 nodes

Part Number:SN65HVD1050

hello TI,

      We meet SN65HVD1050 can't stable communication with 15 nodes in one bus ,  Try to drop rate from 1Mbps to 500kbps, it still can't stable communication.

we see iso11898 standard , the maxim nodes is 30, we want to know what's root cause will lower this nodes, could you provide your suggest?