Jumping back to the OP for a bit. The Iris RE is inconsistent in my opinion because of a very poor antenna design. It is a “hit or miss” depending on your system. Moving the RE a few feet or to other side of a room or hallway will deliver huge changes. The purpose of a RE is to help support devices that are located further away or located in difficult EMI locations. Instead in most cases other Z-wave extenders are supporting the Iris RE. Note: The issue with the Iris RE is with Z-wave. The Zigbee repeater/multiplier appears to be operating as expected.
My recommendation would to not use the Iris “RE”. Any of GE/Jasco/Linear “modules” will be far superior to the Iris design. Keep in mind any device that has to mounted “in wall” will have reduced performance but usually still far better than than the Iris RE. Note: Devices mounted in metal junction boxes will have their range reduced dramatically. The modules that just plug into the wall are your best option if you are having Z-wave range issues.
Show any 10 year old Ham Radio Operator the antenna design in the Iris RE and they will be able to explain why the paper clip folding back on itself design is an extremely poor design and likely the cause of the “hit or miss” performance of the RE. This design will cause nodes causing drop out / weak areas of performance. Depending on local EMI your performance will vary greatly.
NOTE: The poor design will be most evident when users do not have other Z-wave repeaters online. Lighting modules, thermostat when using the “C” wire and the best Z-wave repeater at the moment, the LInear garage door opener. When additional Z-Wave repeaters are online they will support the poor antenna design of the Iris RE.
Another great Z-wave repeater/extender is the thermostat when using the “C” wire. If your system does not use a “C” it is rather easy to add one and there are links on the RTOA website to describe how to add a “C” connection. (Note: the device needs to paired/re-paired with “C” wire connection connected)
While the Iris RE is not completely useless (Zigbee extender/multiplier & for Z-wave if it is in the “spot” or has supporting Z-wave extenders near by), if you are having Z-wave range issues try other RE options.