I don't really buy that Russia has started using Kh-55 cruise missiles as just kinetic impact weapons. That's one hell of a waste of money to do relatively little damage. Yeah it'll still cause damage to whatever you hit, but it's going to be very very localised.

And have we seen anymore since then? I don't believe so.

This really seems like either a test, to see what the performance of the Kh-55 against Ukraine is like for a nuclear attack. Might be as a feint, or just training and decided to point it at Ukraine because why not (this is sadly the most hopeful), or worst of all because they might launch a nuclear attack soon.

I can't think of any other reasons. Some people have said by accident, but the Kh-55 is launched from a plane. Yeah ok I get that a pilot could accidentally launch it, but how do you accidentally load it? Training seems more likely given this, but that doesn't mean it also wasn't a test.