Not with Oneplus, but the same thing happened to me with MS Surface Pro and Huawei Matebook Pro. I used to have eyestrain on Macbook and other screens, but then noticed a different scenario with Huawei - not exactly eyestrain, but rather nausea and feeling of pressure inside my head, behind the eyes. Then, similar, a little bit smaller issue with Surface. And, what's unusual, it got fixed, probably after reinstalling Windows 10.
I no longer get this feeling when using Chrome or Windows in general, however noticed that issue still exist if I turn on a full-screen game. So something must be changing and I guess it's the way some elements are rendered on the screen by games and by Windows. Probably recent updates to Windows and Chrome fixed whatever was wrong, but the problem still exists in older games.