I've come across a bug where loading vehicles onto wagons while the train is on a curve causes the train to disconnect from the wagons. The train is unable to reconnect after ('no rolling stock found to connect' even though the train is backed up to the wagon). The only way to reconnect them after this is to remove all the vehicles, pick up the wagons and reassemble the train on a straight piece of track.

This has happened to me a few times, specifically with a 1 engine 6 wagon train on a roundabout, with spidertrons being loaded onto it.

I have a save with this issue if you're having trouble reproducing, please let me know if you need any other information.

When it gives the "no rolling stock to connect" error, is the wagon correctly loaded apart from that? What happens if you get on the loaded wagon and press "g"?

The API makes it annoying to figure out which directions have wagons that need to be recoupled after the wagon in replaced. It's possible there is a logic error in that code.

Yes, please post the save if you can.

Sorry for the delay in response! The wagon gets loaded properly other than that.
Where would you like the save posted? I'm not sure how saves work when sharing with other people, if it doesn't just drop you in my place you should see a waypoint along the northwest wall marking the train.

Normally people put the ZIP file from the saves folder on their DropBox or Google Drive and share the link. In a single player game, anyone who loads it will share the same character. You can DM me the link on the forum if you want.

Thanks for the save, I see the issue. The curve is actually not the problem, it is the curved switch. When the new wagon gets placed, it gets put on the left leg of the switch (just barely), so it won't couple to the locomotive on the right side of the switch.

This is a known issue with both Vehicle Wagon and Multiple Unit Train Control. I don't know how to fix it other than to make your loading/unloading stations not be on curved switch tracks. The API doesn't give enough options to really select which track of the switch it will be on when you place a new train.