There are two bugs concerning the connection of any Bee module to the Stalker pins to use software serial. The following connections have to be established to use the Bee module with a software serial port (UART emulated in software, library softserial.h):

• solder jumper P6: BEE_TXD → D6 (soft UART RX),
• solder jumper P5: BEE_RXD ← D7 (soft UART TX)

On the official Seeeduino wiki you find one bug reported but there is a second issue. I propose a solution described in the following document:

stalker_v3.0_workaround_p5_p6_2016-06-21_v002_rb.pdf