I wonder if the OP puts on the little valve stem thread locker before he pumps the tire up. Some people eschew the use of that little part but if you thread that little washer onto the stem before you pump you can ensure the valve stem is seated properly. I would also suggest going back to the smaller of the two tube sizes.
I would add that floor pumps that screw on the presta valve don't end up pushing down on the valve when they are attached so even if you think that little lock ring is going to cost you 3sec over 4 hours
they are helpful in this sense. Not as quick, perhaps, but after too many issues with too many push-on floor pumps I got a Lyzene which does take an extra 3 seconds to screw on, and I like it very much. (and the little Lyzene frame pump is fantastic).