I think the problem is in the cad, this happened to me the last time, when you have overlapped surfaces, (surfaces on top of each other) this can happen, so what i will suggest is to let the surfaces intersect with some mm instead of trip them.
I think the problem is in the cad, this happened to me the last time, when you have overlapped surfaces, (surfaces on top of each other) this can happen, so what i will suggest is to let the surfaces intersect with some mm instead of trip them.