Cheers fella, got it working now. Weird one though - if I set it as mobile connection only, and turn off wifi, it works. Yay! But if I set it to mobile/wifi/ethernet and connect to my work wifi - no dice. Could this potentially be due to limitations of my work wifi? It's a guest wifi so maybe there are restrictions? I guess I'll try tonight from a standard home wifi (not my own network) and see. Thanks again, as always!
It's possible that your work WiFi is denying connections on non-standard ports (58050, 58051). If you are not using regular http port 80 and https port 443 for something else on the machine running BubbleUPnP Server, you could try configuring BubbleUPnP Server to use these ports. For this, edit configuration.xml, fields httpPort and httpsPort and set them to 80 and 443 respectively.