When I run react-native run-android, it gives me the following error:
Could not connect to development server
and first of all I appreciate you for posting your doubt. It's mainly because maybe your expo or the app in which you run your react native project may not be in the same local connected wifi or LAN. Also, there is a chance that there is disturbance in your connection frequently due to which it loses its connectivity.
I too face this problem and I personally clear the cache and then restart again and boom it restarts perfectly. I hope this works for you too!