No way. I have used 5mm smaller blades on my kapex and been able to adjust the stop to still allow it to cut through. I find it hard to believe you have sharpened you blade so much that it has decreased in diameter that amount for it not to cut through.
Unless their is a fault I don't think you have reashed it's limit.
Welcome to the forum. I would recommend that you give our service department a call and they can help determine what's going on. Their number is below in my signature. They're open M-F, 8a-5p ET.