Thanks. I see from the example you gave the the Crawley endpoint is the place=town node for Crawley, located in Southgate Playing Field (presumably the approximate geometric centre of the town).
https://www.openstreetmap.org/node/17722928

Oddly, Metrobus's planner seems happy to use a start point in the middle of playing fields, but declines to produce a route unless the end point is changed to Horsham Station (Stop K) or Horsham Station (Stop L).

It might be worth raising this with Metrobus, as it is possible that moving the railway station node will not solve the problem. Even if it does solve it, it is also likely that someone will move it back to its original position.

If you don't have any luck with Metrobus support, you could try asking for help at https://community.openstreetmap.org/