Perfecting my panettone, or the tale of a sad second rise

Good afternoon friends. I'm on a mission to make the perfect panettone, so I'm practicing before the holidays.

I refreshed my 100% hydration starter 3 times over the week before I baked, and the night before I fed 2oz with 5oz of flour and 5oz of water.

First dough went together fine. Beautiful, strong gluten development.

For rising, I put a seed warming mat on the floor of the oven with a baking dish of water on top. It keeps a solid 78-80F in there.

The dough tripled in 14 hours, just as the recipe suggested. So I moved on to the second dough, adding it to the first, kneading, checked for a good windowpane. All good.

Pre-formed loaves, left on counter for 30 minutes. Engaged the la pirlatura for a final shaping and popped into panettone molds.

The recipe suggests tripling in 6-12 hours, but after 13 it had just about spread to the edges of the molds. It was already 1am and I had to be up at 7, so I took them out for 30 minutes to develop a skin while the oven heated up, again as the recipe suggests.

Scored, added a pat of butter, and into the oven for 50 minutes.

It's impossibly soft, rich, and delicious. A hair undercooked despite measuring 200F, so that's a note.

So I'm hoping for theories on what went wrong with the second rise. I have two:

1. It was too dry in the oven and I didn't have the loaves covered, so it developed a skin too soon and stopped the rise.

2. The loaves were too small for the molds and they just spread out instead of rising up. They were about 650g apiece and the mold is 6 5/8" across. I think a 1 kilo loaf would be right for these molds.

But I'd love to hear any opinions y'all might have.

Cheers!