My mother-in-law, sadly now deceased, used to have a friendly rivalry about who saw the first robin of spring. Sometimes I would hear them for a week before I saw one.
And usually every year or two, up here in West Central Wisconsin, there is a newspaper article or TV news story where a local bird enthusiast is interviewed about robins which stay all year around, hidden somewhere in thick woods.
Of all the hunters, farmers, loggers and wood harvesters I've known, I've NEVER run in to one who has seen a robin here in the winter in one of those little groups the naturalists crow about.
Anyway, either your robin is lost or hasn't turned on the cloak of invisibility for winter yet.