I have a few ideas of what could help:
If you are behind a VPN, try disabling the VPN.
If you are using windows 10, run CMD on your machine and type ipconfig. Take a look at the first Ethernet Adapter. If it doesn’t say Ethernet Adapter Ethernet it means Expo is taking the IP address of something else.
To fix this, go to network connections and disable the adapter that it should not be pointing at.
Connect your computer to the network and your phone to the same network. Restart Expo.
Please let me know if this doesn’t work.