I feel like the more likely scenario here is that the third party screens have a cheaper/worse digitizer for the pencil so it just doesn’t track as precisely. I’ve replaced several of my own screens on iPads and iPhones and, unless you pay for an OEM screen from an otherwise dead device, third-party screens are almost always cheaper and less responsive than the original screens on these devices. Why would Apple only do this for diagonal lines instead of just disabling pencil support for third-party screens altogether?