Shake Shack Inc. shares were volatile in the extended session Thursday after the fast-food chain topped Wall Street estimates on earnings but offered a weak-than-expected outlook. Shake Shack shares, which had risen by as much as 5%, traded between gains and losses and were last up 2.4% after hours. The company reported a fourth-quarter loss of $14.4 million, or 55 cents a share, compared with net income of $3.9 million, or 15 cents a share, in the year-ago period. Adjusted earnings, excluding charges from the U.S. tax overhaul, were 10 cents a share. Revenue rose to $96.1 million from $73.3 million in the year-ago period. Analysts surveyed by FactSet had estimated 6 cents a share on revenue of $92.8 million. For the year, Shake Shack sees revenue of $444 million to $448 million. Analysts expect revenue of $459 million.