What I don’t understand about this is that if the blockage is at Craven Arms, why are no trains running north of Hereford so leaving Leominster and Ludlow not served
My educated guesswork would be that the unit workings wouldn’t match-up if they were to have run through to Ludlow from Hereford, making the southbound return workings late. You also have traincrew diagramming to consider, as I expect Shrewsbury would normally be a point where crew would changeover and take their breaks, which instead would perhaps be taken at Hereford during the layover between the northbound arrival and southbound departure.
Fortunately, the line has now reopened.