I think I found out what was wrong with the Soapbox videos I was trying to upload. When I upload videos of WZ I default them to HIDDEN visibility state which means that the videos don't show up on Soapbox when someone does a search, so it's hidden by obscurity.

Somehow yesterday when I uploaded the videos and set them to hidden, they weren't visible to the internet at all, so I just toggled between PUBLIC then back to HIDDEN visibility and everything's fine now.