Good news: I see the same error as many of you (too many keyboards). This will make debugging easy.
Bad news: strangely, Windows likes to keep around multiple device listings for the same device. Why? Who knows. You can see this in your device manager.
Bad news: the input library can't distinguish which devices are duplicates.
Bad news: the input library I've been using isn't being maintained. It hasn't been updated in a few years.
Good news: I think I found a work around. Players will confirm keyboards with the spacebar before playing.
With luck I should be updating a fix in the next day or two. Thanks again for your patience.