I’m having tons of trouble turning left while 1 foot riding right foot down. I call it “turning across” the ride.
Right foot riding and turning right is smooth. (I’m not great at it. Its just smoother)
Right foot riding and turning left is jerky with arms everywhere and typically resulting in UPD.
What is going on here? 
I can’t speak for left foot down, because I can’t do it yet. But I suspect that “turning across” that ride will be similar.
Re: Turning…one foot riding
Sounds like you are in need of more practice. Work on smoothing out the pedal stroke. Though your riding position is not symmetrical, it should be possible to turn in any direction you want. Just tell your body to obey you!
to practice one foot riding, do tight, S’s down the road. not big ones. just swerve. then eventually you will be able to do a really wide U turn and you will make the U turn tighter as you ride more. in my gallery of 3 video’s i have one titiled one foot riding.
I have no problem taking advice from a guy with a cast on his arm. He’s obviously worked out the kinks.
For me 1-f turning is mostly in the shoulders. Try turning your shoulders (and looking) in the direction you want to go.
Also, for “turning across” it has helped me to think about my foot circles and make them full and round. I especially have to reach way down with that outside foot to get to the bottom of the stroke.
Also spend a lot of time riding 1-f, even if it is straight. In order to ride straight you have to make little corrections both ways, which eventually blossom into full turns both ways.
Another thing to do is to bend around an obstacle instead of just open ground.
Every day is different so if you get it today, you may not have it tomorrow, and v-v.