What is this grainy surface on my two-week-old sourdough starter?
Naturally, when you create dough you expect it to rise in size the following few days. That's just a chemical reaction that allows air to enter the dough body and traps it in tiny bubbles. My theory is that if the dough is not as high as expected that the air has escaped it because of the extra time you left it.

The pattern is not unusual and is the result of the deflation I'm talking about.

It's probably still safe to eat, but the bread won't be as good(eat at your own risk)