Could be a specific issue with your input device vs. screen resolution vs. hardware acceleration vs. new features like the artboard rotation vs. being zoomed out from space, a.k.a. mundane precision issues at small scales. Start by turning off GPU-accelerated previews and see if the behavior improves. Anything else will require more info about some of the points I mentioned.
For earlier versions, you may select everything and then untick Align to Pixel Grid in the Transform palette, and also untick Align New Objects to Pixel Grid in the flyout options. It is crucial that the box is completely unticked, not just a - which also counts as ticked.
It may be noted that even if Align to Pixel Grid is unticked with all objects selected, as long as Align New Objects to Pixel Grid is ticked the creation of new objects will result in those new objects being aligned, even when they are created from existing objects as may happen with Pathfinder operations.
You may avoid document types with that as default (RGB for web and the like) or change the default for such documents.