The Class 170>171 conversion was more expensive/time-consuming than first imagined, which Southern weren't happy about
Although it is actually fairly unclear as to how much works they needed, and why so many works were actually done.
Some stories suggest all the wiring was stripped out but in that case why do they still have the wifi transmitters in them?
They were out of service for at least 15 months for all these works, which apparently included corrosion works and a major overhaul. In the meantime the rest of the Scotrail fleet is apparently happily in service day in day out.
The converted Southern units also appear to be incredibly unreliable if rumour is to be believed, giving rise to most of the unit failures. Again oddly the Scotrail ones seem far better.
It's a mystery!
However Southern have confirmed to me they are not planning on taking any more 170s.