Zigbee and Wi-Fi use the same frequency band, and communication failure occurs when communicating at the same time. Therefore, in order to co-exist both sides, it is effective to control not to perform simultaneous communication. The mechanism that controls this is called PacketTraffic Arbitration (PTA).
Silicon Labs' Zigbee-enabled modules include this PTA functionality.

Silicon Labs has published a related application note, so please also refer to it.