BTW, I just tested my Dash Wand, which is associated with the same Amazon account as the Echo and dots. It also works fine controlling the lights just like the various Echos. I'm really thinking at this point that there's a firmware issue with the Show that's causing a problem. I believe the Show runs a different OS than the Echos do (one that's an android derivative).
Is there a way to factory reset it? I wonder if that would help...