All of these things can be true, because Zigbee is a low-powered radio networking standard, and operates across the same bandwidth range as 2.4Ghz WiFi.
Besides changing your WiFi and/or Zigbee channel, the best way to avoid distance / interference issues is to use mains-powered Zigbee devices that can function as Zigbee repeaters.
If using Xiaomi devices, the only Zigbee repeater that I know of people having success with (including me) is an XBee module. I would recommend searching the forums here for “XBee” and also especially having a read through this thread: