185s have various methods of releasing doors at this station, but thanks to company self imposed safety policies/restrictions.
Hence this insane situation that repeats every time a 6 car produces.
Someone really needs to get onto their local MP as its such a sub-optimal solution - it costs the tax payer money and is entirely self inflicted by policy, rather than practicality.
It’s the same at a lot of TOCs and it’s perfectly understandable. If you have a non-walkthroughable unit and there’s a portion that will not open, you greatly increase the risk of overcarrying passengers, and also increase the risk of a door egress being pulled and a passenger(s) self evacuating.
The soloution would be for Network Rail/Northern to extend the Normanton platforms, OR in times like the OP has mentioned, there should be a 3 car shuttle from WKK<>CFD, that supplements the 6 car service and meets with it at both ends.
In my experience you can make 200 announcements, physically walk up to every single passenger and tell them the situation, and you will still have one “the doors didn’t open”. Happens frequently on the Manchester to Liverpool via Warrington trips, despite only the rear carriage being off the platform!
The Network Rail imposed “stop position” for services at Normanton means the rear unit will hang off the platform, so there is no method of opening the doors here safely.