I'm definitely no bread expert, but it looks to me as if (a) your dough was not "proved" for long enough or (b) there was not enough yeast in the mixture or (c) the baking time & temperature were insufficient.
You may also not have your hydration ratio correct which would also give a similar effect. I'm heading towards not enough water (it may only be 25ml out but it can affect it).Does anyone know what this is, please? A few minutes of googling didn’t give an answer.
Thanks.
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