Here we go again! This one is a bit different because I don’t even find a workaround about it.
It has been previously discussed that it is not super easy searching Asana based on custom fields (You can use the main search and add a filter).
How would you search the custom fields when you are trying to add a dependency (Blocked by, blocking)? Looks like there is not even a workaround.
As it is already discussed before, please understand that a “filter” is something that receives a wider input and “filters” out the unwanted. It is counter intuitive even in the main search that the search is not inclusive of custom fields, and then you have to add a filter to “include” searching them.