Like the others pointed out, the problem seems to be the very drastic change between two wildly different hand/arm setups in the middle of a phrase.
Paradoxically, it is your good theoretical understanding of secondary motion that’s holding you back
You should be able to access an upstroke (or double escape) with very little modification of your “primary” setup.
Since your primary DSX motion is already great, the recommendation here would be to try some phrases that have a lot of DSX string changes and only a couple of isolated upstroke changes here and there. Just try to go for it and play them fast from your primary setup, without doing these big shifts in harm position. You may surprise yourself