I created an interrupt with the target station being a refuelling station and the condition being Fuel (any) = 150 Solid fuel
When the train reaches the station and fills up with 150 fuel, the request continuously flashes, as if the train is consistently trying to leave and the arrive at the station. I have attached a video of me replicating this in a testing world
Train interrupt not completing on fuel condition
Re: Train interrupt not completing on fuel condition
That interrupt condition will always be true.
Re: Train interrupt not completing on fuel condition
Just for illustration 
Once one locomotive of the train has exactly 150 solid it will make its way to the refuel station where it gets topped off.
Then it tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
A it is still full it then tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
A it is still full it then tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
A it is still full it then tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
A it is still full it then tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
A it is still full it then tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
...
Your interrupt condition is wrong. It should be "if solid fuel is < 50" goto refuel
Once one locomotive of the train has exactly 150 solid it will make its way to the refuel station where it gets topped off.
Then it tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
A it is still full it then tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
A it is still full it then tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
A it is still full it then tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
A it is still full it then tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
A it is still full it then tries to depart to the next scheduled station.
It gets interrupted because it has 150 solid fuel and redirected to the refuel station (where it still is).
Then it tries to load fuel.
...
Your interrupt condition is wrong. It should be "if solid fuel is < 50" goto refuel