Tuya sensor won't re-join network

[sfgower]

1. 10 days ago, I started using the Tuya Smart App
2. I added two temperature sensors to the network successfully. One of these sensors was a
3. 
   WiFi Thermometer Hygrometer, Indoor Temperature Humidity Sensor with Electronic Ink Display,
4. I could see the two sensors on my Tuya smart app
5. Today I received a 3rd sensor from Amazon and added it to the network. Note that this another Indoor temperature sensor with display
6. I then noticed then my original temperature sensor with display was offline.
7. I removed that temperature sensor from the network
8. I then attempted to add it to the network. I attempted this six times. On each time, the Tuya Smart app could see the sensor but failed to add it to the network.

All of this is very strange, especially as I succesfully added my newly received sensor on to the Tuya network, but I could not re-add my other sensor (an identical product!) back to the network.

I am a loss as to what to do. Any ideas?