When you saw the white tick, did you also open up the Bome Network Pro tool to see if the connection showed there? If the systems are connected correctly, I see no reason why the MIDI would not go through unless one of the appications on either the iPad Pro or the Surface Pro was not sending or accepting MIDI.
I would suggest if it happens again, that you open the logging view within the Surface Pro Bome Network tool to see if you have MIDI activity there. If not then go backwards to the iPad and view the log there in the Bome Network tool to see if the application is sending MIDI out to Bome Network. If not, go back to your application settings for OnSong.
If you see input coming in the Log in Bome Network Pro on you Surface Pro. Check to see if Gig Performer is getting the MIDI information in and that the ports are open. The other possibility is that you may have had another application holding your desired MIDI port open on your SurfacePro.
If it happens again, please send the Bome Network Pro log file.
This posting shows how to find it.
Steve Caldwell
Bome Customer Care
Also available for paid consulting services: bome@sniz.biz