I believe infertility is always a possibility with male fh even varieties that breed true with fixed traits. Most male silks are fertile as far as i know. Let them try again.
I sold that male thai silk as I believe he was sterile I came across another one a few weeks back and put him with her to see what would happen. The two hit it off instantly and 9/9/12 they spawned
I almost didnt think he did his job because the eggs started to turn white but he did and I finally have 20 or so fry that hatched on 9/11. I will keep you guys posted on these guys as I am eager to see what they will look like