Oh boy - you have to figure out a way to break that sleeping posture.
Def not good for the blood flow issues.

Is that with tummy sleeping & arms up, or on your back with arms up?

If on your back- some place tennis balls or knotted socks in the back of their pajama tops to discourage the back sleeping.
same prob will work for tummy sleeping.
How do you do on your side?

oh or keep arms inside of pj top that will keep them down...

But anything to break the habit of arms up like that, we are all re-trainable