My rye bread is flat

I tried to bake this rye bread. I let it rise in an oven with the light on for the first three rises and each time is rises really well, so I don't think the problem is the yeast. But for the final rise, obviously I can't rise it in an oven because the oven is preheating, so I leave it on the counter. And the last rise, I'm not sure it rises enough because I follow the instructions, put it in the oven for 15 min at 450 and then 30 min at 400 and it tastes fine but it's flat when it comes out. I don't score the bread since I don't want to deflate it, and I don't do the ice cube thing, but that should only affect the texture of the crust, not the height of the bread, right?

What am I doing wrong?

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