Same issue here, spent an hour or so with Amazon on Sunday. I got to a tier 3 tech, who gave up and said they would get back to me. (cue the sound of crickets).
I have had to resort to making scenes for lights, as those commands still work. It is only the ON command for devices that seems to have a problem.
As a cold suggestion, make sure you don’t use any beta or development skill.Also try to remove skill, re-install it again, and link it again with Vera.