My understanding is that the maximum resolution the Xbox One’s HDMI input can handle is 1920×1080. While, I believe, the data throughput of line3x 480i would be equivalent to 1920x720p, and the resultant, deinterlaced image would be 1920×1440, and I find it likely that the Xbox One has no idea what to do with either of these, because neither is a standard video mode.
You may have better luck with line4x, which would be a bob-deinterlaced 960p, or, if you don’t like bob deinterlacing or the Xbox One doesn’t like 960p, you should set 480i to passthrough and let the Xbox One deinterlace (and scale, if it does that).
If you absolutely need 480i line3x to work, you’ll need to get a secondary video processor, like the Extron DSC 301 HD or DSC HD-HD, to pair with the OSSC. I have a DSC 301 HD, and it works great with 480i line3x from my NTSC TEST PS2. Just be sure to configure the scaler to output 1080p at either 50Hz or 60Hz, and your Xbox One should have no trouble recording the result.