This is interesting, but I'll throw a little luke-warm water.

The observed high-consistency behaviours were run against temperature=0 API calls. So while both models seem to have the silence as their preferred response - the highest probability first token - this is a less powerful preference convergence than you'd expect for a prompt like "What is the capital of France? One word only please". That question is going to return Paris for 100/100 runs with any temperature low enough for the models to retain verbal coherence - you'd have to drug them to the point of intellectual disability to get it wrong.

I'd be curious to see the convergence here as a function of temperature. Could be anywhere from the null-response holding a tiny sliver of lead over 50 other next best candidates, and the convergence collapses quickly. Or maybe it's a strong lead, like a "Paris: 99.99%" sort of thing, which would be astonishing.