Hi, I was looking at the lists of UK incoming passengers and there are several for Mr A Stevenson with and without his wife coming back from Durban, South Africa. They all list Mr A Stevenson & Mrs A as being Scottish. I looked at the censuses for 1901 & 1911 and it appears that around 1911 he may have been spending more time in Durban.
1901 census:
Alfred St., Dunoon, Argyll
Alex Stevenson age 32 b 1869 Gourock,Renfrew occ: life assurance agent
Georgina Stevenson age 30 b 1871 Glasgow, Lanark
Margaret Stevenson age 8 b 1893 Dunoon
Robert Stevenson age 6 b 1895 Dunoon
Annie Stevenson age 4 b 1897 Dunoon
Williamina Stevenson age 2 months b Dunoon
1911 census:
Cambridge Village, Dunoon, Argyll
Georgina Stevenson age 39 head of house married 19 yrs 8 children 6 living living on private means born Glasgow
Margaret Stevenson age 18 b Dunoon daughter occ: laundry maid
Robert Stevenson age 16 b Dunoon son occ: baker
Annie Stevenson age 14 b Dunoon daughter
Williamina Stevenson age 10 b Dunoon daughter
Georgina Stevenson age 4 b Durban, South Africa daughter
Andrew Stevenson age 4 months b Dunoon son
UK Incoming passengers(some of records):
arriving from Durban 14 April 1900 to London just Alexander
arriving from Durban 30 April 1901 to Southampton just Alexander
arriving from Durban 16 Nov 1906 to London Alexander,his wife and child H Stevenson age 8 b 1898 in Natal according to passenger list records
arriving from Durban 26 March 1908 just Alexander
* I also found this one which is very curious with what Ev has found.
Alex Stevenson
Scottish
occ: coal merchant
age: 69 b 1868
departed: Durban, South Africa
arrived: Southampton, England
on: 29 April 1935
ship: Kenilworth Castle
address in UK: 33 Arragon, Streatham
I do not know if he is yours but it would go some way to explain why he "vanished". Hope something may help, Kim