Thanks everyone for your responses.
He was living in Darley Road in Randwick in 1943 in what today is a six-bedroom house. It may well have been then too - I now believe that it is most likely that he was renting a room, along with other lodgers in the house.
A bachelor, in the 1920s he lived with his married sister and her husband in Bondi for many years. He appears in the electoral rolls during this period. He was then overseas for about five years until the mid-1930s. But he makes no mark on the electoral rolls though between his return to Australia in 1935 and this sole appearance in 1943. He died in 1945.
It now seems most likely, as suggested, that he was lodging/boarding through these 'missing' years. Unfortunately, there seems to be no Rental Board or equivalent records from back in the day. So where he was living and why he chose not to register on the electoral rolls seems destined to remain a mystery.
Many thanks for the suggestions.