There are several issues need to be checked:
1. Set the same communication data rate for both master and slave;
2. Slave VCC need add one capacitor about 2.2uF. If the capacitor value is too small, the master may can't detect it for ringing. If the value is too big, the master can't detect it either because the capacitor is bypassed when start up. It is one capacitor load to the Power line.
3. Master Vcc voltage is lower than 3.4V.
4. Set to lower datarate and longer waiting time to check.