Oh, that is odd. Erm, ideally you'd provide a video forme to get a better idea of it. But if that isn't doable, then could you provide some info about if you play on PC, Mac or android, and where exactly it happens.
Oh I play on android. As for where it happens, every time the fade in effect plays out, so it happens throughout the entire game.
The first screenshot is apparently the standard look. The second one is during a fade in effect, if you look closely you'll notice it's slightly more thicker.
I know it's VERY, EXTREMELY and UNNECESSARILY nitpicky. It's just my observation, and for me it was quite distracting