Search based things come and go and quite randomly, I've found. "£1 in $" is a search I've used perhaps 1000+ times over the years and while it's been consistent for the past year or so, it often used to not return the currency conversion (but alternatives like "1 GBP in USD" did, etc.)
That's usually a ranking problem. Search is one big ranking system even for these custom looking responses. Sometimes they mess those up, or the backend that replies with them is down (ex. They accidentally took down weather once for the whole world).
