Pain De Mie Crumb Issues

I’m not really sure what caused this, but will venture a guess. Did you aggressively push the dough down into the bottom of the pan?

OK, a second guess :-)
Is your oven producing much more heat from the top than the bottom?

I do have a suggestion for pullman pan baking that may interest you. It greatly simplifies pan bread and the crumb produced has been very nice. If interested see THIS LINK.

BTW - most consider a spiral pattern in sandwich breads a good thing. That is always my goal for sandwich pan breads. Crumb pattern looks good to me.

I wonder if you used a bit too much flour when shaping.  That can cause a separation in the crumb especially if the dough isn’t very high hydration.  I see this in my baguettes when I’ve used too much flour, it causes these lines where the crumb isn’t connected that I absolutely hate seeing.

I wonder if you baked low enough in your oven, the bottom crust looks paler than it should be, this will cause the crumb on the bottom to be more compressed as it isn’t rising as well.

Benny

I am not a pan de mie expert at all but I do have a few thoughts. The spiral separation may show that there is too much bench flour on the dough before you shape into a loaf.  Try dusting off the extra bench flour with a brush before rolling.

The second thought is that the dough is not raising quite far enough in the pan so there is more room for bubble expansion. Perhaps a slight increase in amount of dough??....OR.....

I see there is a slight sinking of the top,also. Could be that the dough is just a bit overproofed. It may be a case of less proof (but it looks a bit lower in the pan), more oven spring and smaller bubbles at the top of the loaf as it contacts the lid.

This is a great example of why a crumb shot is almost more important than a loaf shot. A LOT can be told from the crumb.