You might have run into one of the various ST limits.
Model number of your SmartThings hub?
Total number of devices on your ST account?
Total number of Zigbee devices you have? It’s possible you ran out of available parents. This is a common issue with Sengled bulbs, because unlike most Zigbee brands, Sengled bulbs will not parent each other. 
FAQ: 32 Zigbee direct connection device limit?
If everything is working fine now, you don’t have to worry about it, but just in case it turns out to be the physical location rather than the device, or the “next one added”, you might need to start checking limits.
FWIW…