Our beefsteak almost ALL (80% - 90%) develop the sort of cracking / stretching seen in the attached pictures from this morning. It usually starts on the blossom end, but develops up the sides, and sometimes starts at the top. The fruit WILL mature, but usually with a rotted out core (though dry rot-looking, like in the pictures). You can see in the first image that it's starting at the stem as well.
I've done all the research I can, and nothing seems to match my problem. We had this happen to our beefsteak last season too. We're in Southern Ontario, this season has been dry dry dry...so the plants have gotten pretty consistent hand watering. It doesn't look like cracking from too-fast growth. Sometimes there are tiny larvae looking insects in the gaps...but I don't know if they're just enjoying a crack caused by disease, or making the crack itself. There weren't any on this particular tomato.
I'd appreciate any help you can provide!