We do not think this is nutritional. Our guesses would be incomplete pollination/fertilization of ovules, environmental stress (excessive hot or cold temps before or during flowering and fruit set. https://extension.umd.edu/resource/growing-selecting-planting-and-training-strawberries

Marian

Hi- there is a subtle lack of color uniformity that does not suggest a virus or significant nutrient deficiency or toxicity issue. More dramatic and widespread inter-veinal chlorosis could point to an iron or managanese deficiency. You could rule out nutrient and pH issues by having the soil tested (if this hasn't been done in the past three years). 

https://extension.umd.edu/resource/soil-testing-and-soil-testing-labs

We don't think that a nutritional disorder produced the fruit symptom in the photo. 

Please send additional photos if symptoms change or worsen.

Jon