Trains wait in the [Resource Specific] Waiting Bay.
The Mine detects that it has a full load available.
The Mine Controller detects this condition, and acknowledges it and records it.
The Waiting Bay controller sees that a train is required, releases it and notifies the Mine Controller.
The mine controller then subtracts from the number of mines that need service.
The above sums up how it should work and the save attached works that way.
The subtraction has already taken place and now there is a mine that will never get serviced.
I found that the Train Schedule does not update the state (Disabled/Enabled) of the Target Station when it is released from the Waiting Bay stop using
the Wait for Circuit condition (Green > 0).
To see the problem open the save and delete the Train Stop that has the Hazard Concrete.
The problem will show up within a couple of cycles.
Attached Save REQUIRES Creative Mode Mod.
Blueprints for the system are included in the save.
If you use them YMMV as this is a work in progress.