Why does my Apple Watch sometimes charge, and sometimes not?

I have a charging station for my Apple Watch Series 3 and I always put it on at night. When I put it on, it will start charging, put in a few moments it goes back to the main screen (AKA: It isn't Charging). I'll remove it from the charger multiple times and replace it on the charger until it finally continues charging without disconnecting. Why does it do this?