Yang compiles but fails to load

The yang file compiles but fails to load using confd.
Following error is seen:

Failed to load file yang/a.fxs: Module b: The target of the default-ref path for n/int/intfc/ot/vst does not exist

In what case would a yang file compile , but would not be able to load.
Could someone please help with understanding this error.

In this case Module “a” has values augmented from module “b” :

augment "/b:is/b:i" {
        container o {
            when "../if:type = 'iu'";


            uses c:as-pr-k;

n/int/intfc/ot/vst actually refers to a path in module “c”.

It is difficult to see what might be the problem here with the information provided. Is it possible to attach the models in order to reproduce and try to correct the problem?