Lantana callipo Tutti fruiti leaves brown

Hi please can anyone suggest why this Lantana which we overwintered indoors has now had all its leaves turn brown? Was it the shock of being out? We did it gradually over a week. It’s in the same warm sunny place it thrived last year. Also, it has grown on two main stems, should we cut it back? Most pictures online show a bushy shape. Thank you very much for any knowledge!