The one I never got to the bottom of is for the opposite reason - random extra stops.
Back in around 2002-2004, or so, one service from Victoria to Southampton Central via Hove (calling Cosham around 2120) would call additionally at Portchester and Woolston, possibly Netley also, when no other off-peak services did. This would have been in the last years of the CIGs, but I can't remember whether it was Connex or Southern by then. It was the "classic" timetable though, with 1tph to Southampton Central via Hove with a standard calling pattern of Cosham-Fareham-Swanwick only.
Not sure if anyone can shed a light on this. It wasn't to cover a missing SWT service, as one followed around 20 minutes later in the standard hourly path. Maybe this topic (random extra stops in the hourly pattern at off-peak times) needs its own thread!