What are the devices? Zigbee? Is your wireless router close to your Hub? Uses the same frequency so that can sometimes cause issues. Make sure the antennas are not obstructed by cabinets or pointed a less than optimal way (Hub v2 Antenna Orientation)
Overall I have pretty good success. Had devices dropping for awhile (zigbee) but that went away couple months ago. I have lots of zwave light switches so the mesh is pretty strong. I also picked up a few zigbee outlets to boost the zigbee mesh.