Sorry, I don't think I understand you.

If this road is for buses only, then how can `motor_vehicle=yes` be correct? That includes all motorized vehicles - automobiles, motorcycles, trucks, buses, etc.

https://wiki.openstreetmap.org/wiki/Key:motor_vehicle

All these roads have (and always had) `bus=yes`. This allows public service buses.

https://wiki.openstreetmap.org/wiki/Key:bus#As_an_access_tag

To further clarify access tag hierarchy. `bus` is a type of `motor_vehicle` and `bus` value overrides `motor_vehicle` value. In other words, `motor_vehicle=no` or `motor_vehicle=yes` does nothing for buses when there is `bus=yes`. Therefore, if changing `motor_vehicle` matters for GraphHopper, then it sounds like there is a problem in your settings.

https://wiki.openstreetmap.org/wiki/Key:access#Transport_mode_restrictions

Obviously, I don't know what your settings are. I can only tell you what the correct tags are based on your description. And your description of these roads sounds like `access=no` + `bus=yes` - only buses allowed (which it had before).