Have trouble removing rust stains

So I went out today to do some test spots on a upcoming job. The first stop it worked well. The second house we couldn’t for the life of us come out. We used F9 Barc 50/50 mix I’ll attached photos any help would be great. cid:E7868150-D223-47E7-8308-A6E63633D949 cid:C881CF30-492E-4AE0-81F7-E6649A29C712