When you enter the map and begin moving around, there is a chance for it to get 'stuck' in where dragging and moving your mouse won't move around. This usually can happen when alt-tabbing to another computer window.

The way to go about easily fixing it is moving your mouse down to the bottom right where those little arrow icons are and clicking on them. This should fix it.

Can the developers look into fixing it? It can be a bit annoying sometimes!