I don't have any Iris devices, but I used to have ~10 Lightify bulbs, 5 line-powered outlets (Quirky outlink), one GE zigbee dimmer, and three Samsung plugs. Things didn't go so well. On the recommendation of several people here, I got rid of the Quirky outlinks, and added 3 Securifi Peanuts and 4 Ikea Tradfri plugs. My zigbee mesh has been rock solid ever since.
My suspicion is a) that some devices behave better as repeaters than others; b) everyone who says that light bulbs are bad zigbee repeaters is correct; and c) some devices can make a zigbee network unstable - like the Outlinks.
You're ok with the Sengled bulbs - they are purposely designed not to route.
