Terrible Lag When Starting a Scene Which Eventually Resolves Itself... Graphics Card Issue or Unity?

I have an issue that is driving me absolutely mad. The scene I am running seems to have a completely random performance issue.

When I start my main scene I am loading in several other scenes with LoadLevelAdditiveAsync. I have one scene for each terrain tile that composes the region the player is currently in and they are loaded/unloaded as needed. There has always been a performance spike when loading the initial terrain tile scenes as you can see below:

This is not a problem. After this point however, I have a significant amount of lag that drops the game to ~15fps. Stranger still, this lag seems to magically resolve itself after some random amount of time as you can see below:

There is a drastic performance improvement that I cannot explain. Throughout development this is the normal performance level I have experienced (~60fps). Gfx.WaitForPresent is the largest contributor to this fps drop, but I understand that this is for the VSync. It seems like all the other aspects of the GPU rendering are taking up the same proportion of rendering time, but each with much longer times needed to render than usual.

Could this be an issue with my graphics card? Or is there something about my scene that I should investigate further?