Mission Impossible complete!
I did changed out to Märklin current couple instead and soldering wires.
I use function decoder ESU 21 pole.
This time i do use black wire as redirection for the function decoder together with the lighting.
Red wire are power feeder to the decoder from the pick up shoe.
The green wire are AUX1 from the decoder to the lighting.
Now Märklin current couple does not released from the wagons through the S curves (turnouts).

When you see coach lights not working in the middle of a CC connected train, it is almost always a bad ground path and not the supply from the center rail. If that is the case you can either clean the axle wipers or just run them for a while, which almost always fixes that problem. Extremely dirty wheel can also cause one coach to lose its ground path, while the other coaches are fine.

I have also found that many CC couplers will lose any flicker that they come out of storage with after some track time. The contact areas in them are very small but after my Marklin CC couplers settle in, they run perfectly until I pack them away again.

The best I have used are Brawa conducting couplers. They dont uncouple other than by hand but there is no flicker with Viessmann lights. Important to make sure that the power from a slider or the loco is not causing flickering.