This is the train & train stop in question (the dark green train in center left):
screenshot
We didn't narrow down the issue beyond that due to the time-consuming nature of it (every time he desyncs, he's forced to reconnect, which takes about 10x longer than normal, and the game freezes for ~1 minute for me), but we've reproduced it three times now.A world save is attached to this post which was made right before he desynced the third time. What I did was send the long, dark green train to the "War Train North" stop, then re-send it (clicked the arrow in the train UI again) to the same stop while it was moving so that it goes to the bottom train stop, in order to align it perfectly with the loading inserters (since the train has an even number of locomotives/cargo wagons, the two opposite train stops don't line up).
It'll make more sense when you see it.
