I noticed that I couldn’t use a particular attribute in search or set filters. While this can be caused by filter validation I always disable those MPRs (“General workflow: Filter attribute validation for administrator” and “General workflow: Filter attribute validation for non-administrators”) so that never causes me a problem. In this case it turned out to be a naming conflict.
I had bound two “Status” fields to this object type. While they have different Attribute system names and Binding display names, the Attribute display names were the same:
Attribute system names: Status, EmployeeStatus
Attribute display names: Status, Status
Binding display names: Status, Person Status
Once I changed that second attribute’s display name to “Employee Status” and ran an iisreset I could then see the attribute listed and use it in my filters.