Please check if you can ping your router from your PC without OpenVPN. Connect to a different wi-fi (from which you are unable to establish a VPN connection), and try to ping your router using the IP address of your mobile interface (100.x.x.x). Are pings successful? Since your router is configured as an OpenVPN server, it needs to be reachable over the internet, but it seems like your IP address can be behind a CGNAT.
Please, let me know if it's reachable.