Somewhat flat, but the taste is awesome!

This loaf came out somewhat flat, but the taste is delicious! How is my crumb? (First 3 picd are today's loaf). I'm thinking the rise issue is my starter. It didn't double, but it did rise. I made a loaf last weekend (last 3 pictures) with starter that rose, but didn't quite double and the baked rise was great. I've only been feeding with AP. Should I mix with another type of flour when I feed next? My starter is hanging out in my fridge until next weekend.

I used this recipe for both: https://preppykitchen.com/sourdough-bread/