Two railcars as one train

[Andrzej]

Two of railcars on my layout are merged to form a train. Both are in the WDP in the category of locomotive; both have engines, both have own decoders, and both are speed calibrated. Creating them as one train was performed by dragging with a mouse one railcar to the other.
I use it mostly with automatic operation, not often manually. Sometimes it happens that the master railcar is running, the slave is not. I can't find a reason for such behavior. What is interesting, that it never happens when I keep open both control boxes in the WDP. That problem happens when control boxes of both railcars (locs) are closed.
I did cleaning of wheels to eliminate electric connection reasons.
What could cause it?

[Stefan Lersch]

Hi Andrzej,

Creating them as one train was performed by dragging with a mouse one railcar to the other.

where exactly did you do so (in which part of WDP)?

[Andrzej]

It was done according to the WinDigipet_Manual_engl_2018 chapter 14.14.1

Yes, I use WDP 2021, but as you know, there is no manual in English for this WDP version.