PlayStation Javelin After Uncoupling, Then Recoupling Will Not Interconnect (recognises As A 6 Car) Units Again

As in the title. If a 395 as a 12 car unit is uncoupled, then recoupling it makes it act still as a 6 car. Even on the MFD doesn't recognise the other unit.

Is there a special procedure to get both units to interconnect? Or is it a..... BRAVO, UNIFORM, GOLF?
Thanks in advance.