<t> Glad to help! The white dots mean that they're not connected to the rest of your rail network. Follow the white dots back and the point where they disappear and the rail lines become solid green is where your issue is. You'll be able to see there whether it's damage, enemy zone of control or ...

<t> The other thing it could have been was a break in your rail lines. If you toggle rail damage on did you have white dots in the green circles? Sometimes it's not obvious that it's not a continuous track, e.g. the loop around the top of Kaunas. While you were dropping supply one of the non ...