Assuming you're both on AMD GPUs (just a hunch), what drivers are you guys using? I have had that type of issue, especially with turning and moving into crowded areas with newer AMD drivers (R9 380 here). I went back to the last "stable" release (16.3.2) and no longer had any of those issues. So far every new hotfix and update since 16.3.2 has had that issue for me, so I'm staying put for a while.