My Display 2 is an old LCD monitor, Samsung SyncMaster 913V. This website lists its "Native Resolution" as 1280 x 1024. It fails to maximize programs perfectly. You can see below this problem with Notepad and Paint. I see that the 913V recommends 1024 x 768, but this makes everything look too big, so I picked 1920 x 1080.
https://superuser.com/a/1542311 didn't solve my problem, which doesn't happen on my Lenovo IdeaPad Y700 laptop, my Display 1.