I got the similiar issue, and resolved it by the following. The issue looks not related to the Route definition but definition of the parameters, just need to give it a default value.
----Code with issue: Message: "No HTTP resource was found that matches the request URI
[HttpGet]
[Route("students/list")]
public StudentListResponse GetStudents(int? ClassId, int? GradeId)
{
...
}
----Code without issue.
[HttpGet]
[Route("students/list")]
public StudentListResponse GetStudents(int? ClassId=null, int? GradeId=null)
{
...
}