I have a steam tug connected to 2 barrel barges.
When I stop looking at it for a while and go do other things then come back to check, the barges have disconnected.

What I expect is that it has to do with chunks loading/unloading.

I tried this with both the tug registered and not registered.
I am playing on a locally hosted server with ATM9 version 0.2.57

Adding more info as I find more: In all cases the tug continues by itself. Only the vehicle links disappear. I will look into chunk optimization mods that might be contained in the modpack