Larry, It appears you have your joints oriented correctly. I use pocket hole joints constantly, and, only occasionally have a problem with the joint holding. From your description, I'm 95% sure you're stripping the threads out driving the screws. I've learned that I need to drive them with my 12 Volt and not let it crank them down. The Dewalt 20 Volt will strip them almost every time. As others suggested, finish them by hand, if you use that type of driver.
On a side note, when building cabinet carcases, I always drill pairs of holes in each location. That way, if I do strip a hole, there is another available.