You are me. I have similar problems, and 4 Xbees. I notice the xbees for some reason can drop, and when they do, they take many devices with them. I use markus's driver that has presence and lets me know when an xbee drops and I can fix before it starts the avalanche.
Both Ken & I have lots of newer Smart+ bulbs without issue. Check your FCC-ID on the bulb, and use your ST hub to update the firmware if needed. The newer (ZHA) bulbs are DZO-AETHER, the older IQ_Home will cause issues
PS- The hub has a nasty habit of changing the PAN ID, and when it does, you're in for hell. Take alook at yours and write it down, watch to see if it changes
