Separation and oil pooling
Updated
A layer of oil on the surface of a setting batch, and a lye-heavy layer under it.
Oil on top, and worse underneath
The batch splits: free oil rises and a lye-rich layer settles.
Which means the bar is not merely unattractive. Part of it is over-superfatted and part of it is lye-heavy.
It is the failure most often confused with a cosmetic one and it is not.
The real cause
The batch was poured before it emulsified. That is nearly always the answer.
Usually because of false trace: hard oils solidified as the batch cooled, the mixture thickened, it looked like trace, and it was poured at an appearance rather than at a state.
Less often: a fragrance causing separation, or badly under-blending a large batch.
Why it is dangerous
A lye-heavy layer is caustic, and it is not evenly distributed, so a bar cut from the loaf can be fine on one face and harsh on the other.
Which makes a separated batch a disposal or a full rebatch rather than something to trim and sell.
Fixing it
If caught immediately in the mold: scrape it back into the container, blend to genuine emulsion, and repour.
If caught after setting: rebatch. Grate it, melt it with a little liquid, cook it through, and mold it. Rustic, and it is soap.
Prevention is the whole answer: blend to a state rather than to an appearance, keep the batch in its temperature range, and be suspicious of a batch that thickened while cooling rather than while blending.