Jumpy grid in side view

Since my last project, I’ve noticed that when I zoom in while in the side view with perspective mode active, the grid will ‘jump’ around. Meaning that the objects that were level with the grid are no longer level with the grid they are either half a unit off above or below to the sides.

Front and top views don’t produce this effect; and the effect becomes more apparant the more you zoom in.

Anyone else know what is causing this issue?