Game objects appear in game view but not in scene view?

My Unity2D project has been working well, until today when the game objects suddenly disappeared from scene view but in game view it was still there. I've tried restarting unity, and that did not work. When I googled, I mostly saw answers for when the object was in scene view but not in game view, which is the opposite issue from what I am currently facing...

In hierarchy, the game object names show up, but they are not rendered. When I click it, i see only an outline

My camera is in default layer, while the missing game objects not rendered in scene view belong to either the default or UI layer. The only thing that gets rendered in scene view are prefabs instantiated from my script during runtime, as can be scene in the image below...I suspect I may have disabled the rendering in the scene view somehow, becuase when I dragged a brand new game object into the scene, it appears in both the scene view and game view. It is the existing game objects that don't show up. Any idea what may be the cause and how to fix it?

Did you accidentally hide either the objects themselves or the layer they're on?

• In the scene hierarchy, hidden objects have an icon of a crossed out eye (). Make sure your objects don't have those.

• For layers, there's a "layer" dropdown in the very top right of the main Unity window, make sure that the layers aren't hidden either (same crossed out eye icon )

For reference, Unity - Manual: Scene visibility