Bad print

I have a crew called Audiopharmacy in oakland. We’ve ordered a few shirts from sticker mule and the first ones everybody was happy with. Last time we ordered a few white shirts (“heal together rise together”) and you could visibly see the heat press leaving a yellowish stained border around the art. The shirts became pajamas since folx didn’t want to wear them in public. We figured that it was the white shirts that would be have the print problem. Now we ordered black shirts to give it another try. Same issue. The border on the upper side is highly messy. I can send photos if need. Not sure why the first batch came out nice and every batch after had been terrible. Not sure how to fix this other than not ordering any more. Thnx