I get the test card when I turn the OSSC on. I’m not really sure what happens when I use one of the consoles I’m having trouble with. I can switch back and forth between passthrough and line2x and sometimes it will display a garbled frame of line-doubled graphics but freeze on the screen, and it isn’t coming live from the console. It’s just some random frame that it somehow still has in memory or something, usually with the image rolled halfway up the screen. Sometimes I also get the test card when I switch to line2x.
Line2x works fine for some systems like I said, but I hadn’t read of any sync problems with Genesis so I’m surprised it isn’t working either.