There's something odd happening with Single Pass Instancing when a camera is updated in some way. I've seen this repro a few times and can't nail down exactly what kind of changes with the camera is causing this but the easiest repro I've found so far is to just select a camera in the editor UI while in play mode and looking at a Text Mesh. I've also seen this repro after loading a new scene with multiple cameras then returning to the text mesh scene bot in the editor and in a stand alone player.

Once in this state viewport scaling breaks too.