It is not up to your bank to figure out which claims can trump the status of federal benefit payments.
If a garnishment is accompanied by a "Notice of Right to Garnish Federal Benefits," then the garnishee bank can proceed use its normal processes without regard to the presence of federal benefit payments. Translated, an agency charged with collecting child support is empowered to attach such a Notice, but if they do not you must calculate the "protected amount" etc.
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.