Maintaining a contact point on the A string
I've noticed that when playing on the A string in the lower half, especially in higher positions, the contact point can greatly waver, even while keeping a straight bow. Normally it doesn't cause too much of an issue but in positions higher than 5th position, the contact point getting too close to the bridge causes some very scratchy sounds. Does anyone/has anyone experienced an issue like this before?
I think that's every string everywhere...
If you have long arms (especially long forearms) it can be difficult to keep the bow moving straight closer to the bridge. Angling the violin more to the left can help (as can playing viola instead :-)).
What is not mentioned often enough is the position, the trajectory of the right elbow. When you get it correct the right elbow will trace a V-shape in space. The farthest back it will be is at the midpoint, where the forearm-upper arm is at a right 90o) angle. Use a mirror to train that.
A good luthier can make it easier for you to play on all contact points with less scratchy sounds. My violin improved a lot just by cutting away a minimum amount of bridge wood.