There are several things that can cause what you’re experiencing and yes interference is one of them. One of the first things to try is rebooting… everything including the hub. If interference is your issue some devices will report a rssi value. The value is always negative (closer to 0 is better) and -40 to -60 is fairly normal but -75 to -100+ is low and would indicate an interference or range issue. I find this chart works well for both zwave and zigbee devices when trying to estimate range.
Other things to help reduce interference is keep your hub away from all microwave ovens and non zwave/zigbee wireless devices. This includes your WIFI router, baby monitors, speakers and xmas lights.
A faulty device can also cause this and can be very hard to to find, but a device in the throughs of death can cause the zwave or zigbee mesh to hang. Find it, remove/replace it and all will be right with the world. You may have to power off 1 device at a time to find it.
