There's been tons of discussions around it. Basically, depending on how you have your WiFi setup, you want your Zigbee channel as far away from your 2.4ghz WiFi channel as possible. The usual recommendation is to have 2.4gHz Wifi on channel 1 and Zigbee on channel 20.
However, I don't think that's your root issue. You mentioned Lightify bulbs. If you can replace them, do it. Most likely, they are the cause of your Zigbee mesh issues. Lightify bulbs are nasty repeaters that will destroy a good Zigbee mesh in a matter of hours or days. They are notorious for locking up (especially on a chatty mesh) and will take almost everything else down with them. If you can, replace them with something non-repeating like Sengleds and add some mains-powered repeaters.
