How do I fix an uneven crumb?

After struggling with pancake loafs I made some adjustments and I think I improved on my flatness problem, but I still have an uneven crumb.

As you can see, very uneven, mostly big air pockets near the top and small ones everywhere else.

I loosely followed Kristen's method.

500g bread flour (Robin Hood)
360g water
100g leaven (fed 1:2:2 about 3 hours before, bread flour and rye mix)
10g salt

I did a 3 hour autolyse, then added the starter. 30 minutes later I added salt.After that I did a stretch and fold, lamenation, followed with 4 stretch and folds. All of these had 30 minute rests between them. After 45 minutes from my last stretch and fold, I preshaped it, followed by a 30 minute bench rest and gave the dough its final boule shape and proofed it in a banneton for about 90. The dough was fermenting around 74F for approximately 7 hours. I then baked it in a dutch oven 20 minutes with the lid on and 20 minutes with the lid off. My initial thought is it was a combination of under proofed and poor folding and shaping technique. My reasoning is that I saw no obvious signs of strong fermentation (no bubbles). And when I did the finger poke test, the dough sprung quickly back for the first 45 minutes. And/or maybe I didn't pop enough of the large bubbles. The bread tasted great so overall I'm happy.

7 hours seems like a very long time at 74 F. Looks like overproofing.

I agree.

The BF on this 800gr WBF loaf was 3.5 hours followed by a retardation of 12 hours. My kitchen temp is 68~72°F and my refrigerator temp is 38°F. Put into the preheated Dutch oven cold.

There was some minor bursting from underfermentation (I think) but otherwise good performance from the ingredients. At about half the 7 hour time frame you used.

Good work on your loaf. I'm still struggling with repeatability after nearly 3 years.

wow beautiful loaf. I'm making a new one tomorrow, I'll cut a couple of hours off of the fermentation time and see what I get. Thanks.

Two things you might find helpful for tuning BF: (1) using bwraith's spreadsheet; and (2) using an aliquot jar. The spreadsheet uses a simplified model to measure the impact of temperature, salt, and prefermented flour (PFF) on fermentation time. It takes a little time to configure, but I have found it to be useful to set basic expectations in a range of temperatures. The aliquot jar can be used to fine tune relative volume changes during BF if you aren't using a graduated bulk fermentation container.

I am new to this site, but I have been baking sourdough for a while so here are some areas you may want to look at as possible issues. 1) Your levain is not ripe, with 1:2:2 feeding ratio, it will take at least 6 hours at 74F to get to full potential. That could be the main reason for the pancake effect. 2) You may be introducing a lot of "artificial" bubbles via stretch and fold, or with how you are working the dough. These large bubbles are usually pockets of air that form during folding. So every time you do a SF, try popping these bubbles. 3) You may be working the dough too much, and effectively killing the real bubbles. Try one lamination and three stretch and folds (you are working with a strong flour already) and give the dough some time to rest before shaping. Also, I would say 6 hours bulk time should be enough, with another 30 min in banneton after shaping. Hope this helps.