Hi there!
First of all, if you have the wind turn on, turn it off, as that can become too much for the shuttle to handle, and it doesn't help in this case.

On to the problem: you are experiencing a real condition, that AFAIK never actually happened in flight, called aileron-rudder force fight. Basically, the rudder in addition to yaw also causes roll, and the ailerons cause yaw, in addition to roll, and these effects can combine and saturate the rudder. This puts the vehicle into a sideslip, which bleeds off speed. It seems SSV is too susceptible to this effect, especially when turning at low speeds (<240 knots), which with the resulting speed loss, just makes things worse.
You can recognize this situation by looking at the ADI yaw error needle, which usually should be near 0, but in this case will be off to the side. Also, in the VERT SIT displays, the rudder integrator reading ("RUD") will be showing 6.0 in this situation.
To get out of this, you need to use the rudder pedals to yaw the vehicle back to front. This will also cause a roll, so beware of that.
I still don't what causes this, probably a wrong signal somewhere or a wrong angle being used... we have to live with it for now.