Something has likely damaged the bark somewhere below the part that didn’t leaf out.  Look at the stem down below the unleafed area to see if voles or mice have chewed away the bark…probably over last winter.  If it hasn’t leafed out bu now, those branches never will and should be cut away.  There is no need to prune it every year but you can cut it back no more than 1/3 of the total branch structure to keep it fuller…your option.