Im getting this message when using this mod with "Mini trains" mod: "ERROR: The Build Train is not the fully build train, please report this to the autor!"
I can get trains if I manually take the locomotive and join with the wagons, so the problem maybe be in the size of the mini-trains, i'll leave the save file:

https://drive.google.com/file/d/18eyLvwudsPv7j5q2GPgL0q1eb2Z43V46/view?usp=share_link

There is a zone for building trains, you can reproduce the error there using merely mini-trains

Hi,

I fear that there is no quick fix for this, we check if the build train is complete and attached to each other. The issue here is that the trains are created in the center and therefore are not close enough to autoconnect.

Sorry but for now we are unable to fix this issue.

Kind Regards
Voske

Oh, the error misteriously dissapeared one day, sorry I forgoted the post xD