When I bake a 2lb loaf, the very Centre of it lacks structure

Am I over proving my bread, or might there be some other issue? I'm using a fairly standard baker's mix. 750g flour, 450g water, salt, quick blend yeast (Doves).
I bulk prove for 40 minutes, then shape reasonably tightly and into a large, heavy duty loaf tin. 30 minutes in the oven at about 200 degrees c. (Fan oven).
You can see this effect in the image, where I've held it up against a light.
Best Answer
I think everyone who bakes bread has had this issue at some point.
Two key things:
Make sure the bread is fully baked before removing it from the oven. Use a probe style thermometer to check the middle of the bread. For a sandwich style bread like you've shown above, the internal temperature should be about 195-205?F.
Let the bread cool fully before cutting (30-60 minutes). When you remove bread from the oven the interior is partially in a gel-like state... It will continue to cook and the internal structure will stabilize as it cools and the water vapor redistributes throughout the crumb. As tempting as it is to eat warm bread right out of the oven, cutting into the loaf immediately will guarantee that some portion of the center will be undercooked.
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Why does my bread loaf sink in the middle?
Baking temperatureIf the oven is too hot the loaf will be brown and crispy on the outside but doughy in the middle and may collapse as it cools. When bread is baked at too low a temperature it will not rise enough in the oven resulting in a dense and sunken loaf.Why does my bread flatten out?
If the loaf has a flat top then you may have used flour which is too weak. Always use strong bread making flour. Other potential reasons for this problem could be that too little salt was used, the dough was too wet or that the dough was poorly shaped.How do I keep my bread from collapsing?
Bread that Falls or Collapses Can Be Caused By:Too much liquid \u2013 Try decreasing water or milk by one to two tablespoons. Remember to look at your dough after a few minutes of kneading and see if it's a smooth, round ball. If the dough is too dry add liquid a teaspoon at a time until the dough balls up.Why did my bread turn out dense?
Dense or heavy bread can be the result of not kneading the dough long enough. Mixing the salt and yeast together or Losing patience in the middle of molding your bread and there is not enough tension in your finished loaf before baking.57: What is a 2lb Loaf Tin? - Bake with Jack
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Answer 2
Make a smaller loaf; or start the bake at a low temperature and finish high to brown. Slitting the top of the loaf before baking will help as well.
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Images: James Wheeler, Andreea Ch, Pixabay, NOHK