I want to emphasize that the verse “sabbe sankhara dukkha” made more sense to me when I saw it as “all sankhara LEAD to suffering” rather than “all sankhara ARE suffering.” When you said it is “all sankhara ARE suffering” I went back to square one and became very confused and more questions arose. Perhaps others can help me understand as well.
Bad kamma vipaka is a major reason for our suffering in this world. But if the verse means “all sankhara ARE suffering”, then that means bad kamma vipaka is not implied in that verse. Because bad kamma vipaka is not sankhara but something sankhara can LEAD to.