Smart Plug disconnected from network (other plugs in home did not). Tried simple turn off/turn on but no joy. Finally reset to factory resettings and configured as a new device. Device setup up in "Local Only" but when trying to set for Remote Control, kept getting a "DNS Fail" error. After several retries found someone with similar problem had reset his router DNS to Google's DNS IP address (220.127.116.11).
Went into the settings of my home router (Netgear Nighthawk), turned off feature to get DNS from ISP (Verizon) automatically. I continued to use the primary DNS address from my ISP but added a secondary IP address 18.104.22.168. After router rebooted, I tried to reset the Remote Control option, but continued to fail. However, I still got notice from Alexa app that the smart plug was available. I did a quick search for the plug in the Alexa app, found it and added it to the appropriate group. All seems to work now.