WiFi and #Thread/ #Zigbee networks use overlapping ~2.4Ghz frequencies, and interfere with each other.
I've learned it the hard way. My old gadgets kept losing WiFi connection, so I bought the biggest baddest WiFi router. It made everything way worse!
The router kept picking an "unused" WiFi channel 1, which was the same freq as Thread channel 11 that my HomeKit hub picked for its network. Stronger WiFi kept collapsing my Thread network, and knocked even more devices offline.