According to Wikipedia's page for Southern, Class 171s operate on the main line between London Bridge to South Croydon. However, the page for South Croydon station says all services are operated by Class 377 EMUs. I don't get why they would run diesel trains on a part of the line that is all electrified, if 171s even operated there.
It does seem unlike Southern to terminate services at South Croydon though.
It does seem unlike Southern to terminate services at South Croydon though.