Frying donuts split along the sides

I'd guess your doughnut dough was too dry.

I've seen doughnuts with a pale ring around the sides, I'd guess it came from either less contact with oil (if floating fairly high) or from the sides stretching as the heat made the dough puff up, which meant less direct oil contact for the newly stretched dough surface.

For dough to split instead of stretch while cooking, I'd look to similar reasons this happens, eg, in bread - which can include being dry (and especially the surface drying to form a skin, which doesn't stretch), not rising enough beforehand so the "oven spring" is overenthusiastic - which might be a cause for yeast doughnuts though not other varieties, and so on.

With the information that those who tried the doughnuts found them "dry" and "crunchy", I'd go with my first guess of there not being enough moisture, so the dough wasn't flexible enough. If they sat out long enough to form a dried skin, this would be especially likely to cause splitting. Moister dough, or keeping covered better, or brushing with water, etc just before frying, might all work to ameliorate this problem.