Was trying to shunt some DlxTrains hoppers with the blue Diesel
Locomotive from AdvTrains Freight Train and noticed that after bumping
into the hopper and stopping, I couldn't couple to the hoppers. I
reviewed the code in those train packs and noted that they did not
have coupler type definitions, which rules that problem out. Same
thing with construction train (subway reskin). Old German Diesel from
moretrains has no problems.
I noticed then that when approaching the hopper slowly, there is a
range where the couple entities show, which then disappear when the
locomotive gets too close. Bumping the hopper will get too close; a
gentle stop and you can still couple correctly.
Being on a curve seems to be the source of problems. The problem
occurred only when the hopper wagon and shunting locomotive were two
curve nodes apart (cr - st - cr). A single curve involved or a
straight track had no issue. The Old German Diesel having a longer
wagon span probably also affects the problem.
Minimal example world using Blue Diesel Locomotive and Hopper Wagon on
Devtest is provided below as .tar.xz. Must remove dyes and default
from the dependencies of DlxTrains. Then try it with the German Diesel
and notice there is no problem.