Odd outcome when making/baking wheat boule

Hello all ... I recently signed up and this is my first post. I'm fairly new to sourdough bread. I have a 4 month old starter that given 8-10 hours at room temp will increase ~150%. I use 1:1:1 when refreshing with 50/50 whole wheat/bread flour. Ive had a go at with various sourdough bread recipes on the net with varying degress or success but decided to work on a basic sandwich loaf and a basic artisan loaf until I understand what's going on. 

Last week I made an artisan bread wheatfollowing Patrick Ryan's recipe 400g wheat, 160g starter,230g water and 5g salt. Knead to windowpane, bulk ferment 3.5 hours, shape and cold ferment overnight ~12 hours. There seemed to be minimal rise in the bulk ferment and I thought perhaps I over kneaded the dough. Patrick said 3 hours I gave it 3.5 then shaped it put it a banneton then into the frdge. There didn't seem much more rise in fridge and I thought perhaps I overdid my bulk ferment. Nevertheless I scored my boule put it a pre-heated dutch oven (DO)in the oven with an good misting of water. At 20 minutes I removed the DO top and it looked like I had a white pancake at the bottom. However, when I removed the bread from the oven 23 minuts late with and internaltemp of 97C it turned out the indeed was spring but a pale somewhat soft crust.

The crumb looked good and it tasted good albeit somewhat like a bagel. I've never had anything like this happen when making a boule before although my daughter thought it was great and wants another this week. I would appreciate any comments with regards to the soft light couloured crust as well as the late spring with top off the DO.