It is a known issue but I'm not sure if there is a fix for it. Based on what I've read it appears to be an issue with how the OS sees the adapter. I believe it sees only one device when the adapter is actually two devices (regardless if you have two controllers connected or not). I'm pretty sure it's just a matter of fixing a driver and I thought I read that a future release of recalbox will fix it. The problem is that the author of recalbox got a new job and he doesn't seem to be as active with the project anymore, it sucks but it's understandable.