Cursor Drag Lock
I've just upgraded from a 10+ y/o MacBook Air, which didn't have this problem.
Here's the method I'm used to using: You have your thumb resting on the trackpad as you scroll with your pointer finger. When you want to grab and drag a window, you depress your thumb and move it with your pointer, then you release your thumb when you're done and the window stops dragging.
On the new computer/ OS, you need to break contact with the trackpad with your pointer, even after releasing your thumb, or you end up continuing to randomly drag your windows around. This bug messes with workflow quite a bit, as you may not take enough pressure off and accidentally keep dragging. Why require additional work to stop doing something, anyway? Is there a fix yet?
MacBook Air 15″