It sounds like the ERR_SSL_OR_CIPHER_MISMATCH is showing because your public-facing site can’t establish a secure connection from certain networks. Since you mentioned it works on mobile, it might be your router or local network caching an old SSL configuration. Try clearing your browser cache, restarting your router, or checking from a different network. If the issue persists, contacting your domain provider (123-reg) to verify SSL settings can help.